Click Here to reference Sportster VIN Information (including engine numbers) in the History section of the Sportsterpedia.
Click Here to reference the Oil Tank Lines and Routing page in the Sportsterpedia.

From Moon Wolf on modifications. ¹⁾
Modifications were very common (on these bikes). I would guess about half the frames you run across have the ears cut off.
In the sixties and seventies, everyone was running chopper seats and the ears got in the way of the flat look we were after, so we hacked them off (sorry).
In those days, we were anti-brackets and anti-protuberances of any kind, so in many cases the large tank-mounting-boss below the ears went with it.
(along with the front boss for the damper, crashbar mounts and so on)
The guys that did so weren't idiots, they were just doing what kids do. Modifications often started the day you brought your new bike home.
As for me, I know that in 1969, when I bought my 1961 XLH, it took me about four weeks to make it into a near perfect XLCH clone.
(fenders, tanks, shocks, headlight, and magneto and then another year to turn it into a full blown chopper)

1952-1976 frames will interchange. Short frame was 52-66 all and 67-69 CH. Long frames were the other years / models. ²⁾
To change from (long or short) frame you need: frame, swing arm (also long or short. It's the swing arm that varies the wheel base), driver peg supports.
Using the short frame with hump (long fame) motors will require some kind of solution of side stand contacting primary drain plug and boss.
The primary drain is a hump motor thing. To integrate it's addition to the cases, the foot peg mounting points and kickstand tab were moved forward on the long frame.
Hence the different driver peg supports to bring the pegs back into position.

This is a quote from Moon Wolf regarding short frames:

The XLH and XLCH frame are essentially the same frame thru 1966. ³⁾
The XLH has some extra mounts but you could make an convincing CH frame out of one of them quite easily.
The “dogleg” H or “long” frame debuts in 67, and provides additional room for the electric start apparatus, which also debuts that year along with the one inch longer swingarm.
Whatever language you choose to use, the short frame and magneto more or less signify what we guys from the 60s think of when we hear the term.
In 1970, the CH gets the long frame and a timer in place of the mag–two of the reasons some old timers feel that 69 is the last year for true CH.

• L1973-1976 frames were sold for replacement for 67-72 XLH and 70-72 XLCH using Frame Adapter Kit (47385-75).
  The kit includes:
  • Frame (47014-73), has no provisions for the solo plunger seat or springs.
  • Ignition switch bracket (47386-75) for use with pre-72 models without one.
  • Coil bracket (47387-75) used if needed.
  • 2 brackets, bolts, washers and locknuts.
  • Not included:
    • 1970-1971 XLCH (bolt-on) oil tank upper mounting bracket (62554-72).

The early 1973 frame doesn't have the angled bracing welded on the rear.
There was a also a kit (47420-74) to adapt it to the L73-up model frame via a recall.
Click Here to see more on this kit in the Sportsterpedia.

Click on any pic below to enlarge:

The same seat casting was used from 1957-1964 on XL, XLH, XLC and XLCH models. ⁴⁾
Likewise the 65 seat casting was used from 1965-1966 XLH and 1965-1969 XLCH.
This version has the flat boss on the right side underneath for 65-66 XLH coil and 65 (only) regulator mounts.
In 1966, an angled bracket was welded underneath (XLCH models only) to support the 66-up XLCH lunchbox oil tank.
Both casting versions have 2 bossed holes under the right side for the 57-66 XLH “kidney” oil tank.
Casting number underneath (47658-52) on both versions.

57-64 XL, XLH,XLC, XLCH Style Seat Casting 5)	65-66 XLH and 65-69 XLCH Style Seat Casting 6)

Seat Mounting Ears:
The distance between the seat mounting ears is 1-5/8“. The inside of the ears line up with the outside of the main tube.
The bottom of the ears line up exactly with the seat casting. Measuring from the end of the main tube to the tip of the ears is 7-5/8”. ⁷⁾
V-twin sells the ears prefabbed.
The 'bottom' hole on the seat casting is for the rear mount of a 'turtle tank' or any of the large capacity K model/XL/XLH fuel tanks going back to 1952. ⁸⁾

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1957-1981 Sportsters use the same jiffy stand weld-on bracket part# (50048-56). The casting number is 50047-52.
In mid 1967, the bracket was given extra beefier welding with for more support.
In 1977, the lower frame cross-brace was changed (no longer using that area for footpeg mounts).
A round tube was used instead of the original to connect and brace the left and right tubes but the jiffy stand bracket remained the same.

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There was only one factory frame part number for 56 KH and 57-64 XLH (47014-56).
The 1966 frame (47014-56A) was then also sold as a replacement frame for 56-65 KH/XL/XLH models.
Frame features:

• XL and XLH models required a battery and coil and there are 2 bosses on the left seat post for mounting the toolbox/coil cover.
• There is a bracket on the right seat post (AKA, Wedding Band) for mounting the XLH “kidney” oil tank.
• There are two threaded holes on the bottom right of the seat casting for the oil tank also.
• The XLH had the large gas tank and there is a hole under the seat casting below the seat perch for mounting the gas tank bracket.
  The backbone for these year XLH models did not have any holes in the backbone for mounting a gas tank.
  Any holes found drilled into the backbone would normally have been done by the owner and not sleeved.
  XLCH had a factory hole drilled and “sleeved” for the gas tank mount.
  

¹⁶⁾

There were two frame part numbers in the parts books (1965: 47014-65, 1966: 47014-56A).
The -56A frame was sold as a replacement frame for 56 KH and 57-65 XL/XLH models (so it fits 56-66 models without further modifications).
In 1965, certain changes coincided with converted from 6v to 12v systems. 2 small 6v batteries in series were fitted in the same space as the previous single 6v battery.
The battery tray was made into a “Z” shape and fitted both the 6v batteries.
1965 & 1966 XLH frames have 3 bosses on the left seat post (2 for mounting the toolbox/coil cover and 1 for a voltage regulator mounting point).
The coil was moved up under the seat on the right and two angle brackets (31727-65) are used to bolt it to a boss under the right seat casting.
These frames also have the “Wedding Band” strap on the right post for the oil tank bracket (as well as two threaded holes on the bottom of the casting for the oil tank).

The frame below is missing the Jiffy stand bracket but you can see the bracketry on the seat posts.
The coil mounting boss is also visible on the right under the seat casting.

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The 1958 XLC was a one year only bike and shared the same frame as the 58-65 XLCH part# (47014-58).
With no battery or need for bracketry otherwise, the seat posts are both bare with no brackets welded to them at all.
This frame uses the XLCH “horseshoe” oil tank attached to the frame by a bracket that sandwiches the seat posts from the rear with a lower bracket on the motor.
See the link above for the oil tank page.

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The 65 frame part# is (47014-58), same part number as previous year XLCH models.
However in 1965, the seat casting had a change to where a flat boss was made under the right side at an angle but the frame part number didn't change in the parts book.
For 65 XLCH (only), the voltage regulator was mounted there by a bracket (74525-65).
The bracket bolts under the seat and angles across to the left side of the bike above the oil tank where the regulator appears.
This is the last year of the horseshoe tank.

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Frame part #s: 1966-1967 XLCH (47014-66), 1968-1969 XLCH (47014-66A).

• 1966-1969 XLCH used the same seat casting as the 65 CH with the flat boss under the right side but the that spot wasn't used any longer on XLCH models.
  The boss is still there but the holes were reportedly not tapped. The voltage regulator was moved to the left seat post.
  
• (66-69) There are 2 bosses welded to the rear of the left seat post for mounting the voltage regulator.
• The right seat post remained bare (no brackets required).
  
• In 1967, the MoCo added a two point wiring terminal (71561-67), used on 67-69 XLH and XLCH, as a splice block for the tail light wiring.
  On 67-69 XLCH, the plastic terminal is attached to a boss on the left seat post below the voltage regulator with 2 screws.
• 1966 was the first year of the “lunchbox” oil tank.
  An angle bracket was welded under the seat casting as the top oil tank bracket with the internal angle facing the front.
  The bracket being factory welded, there was no replacement bracket listed in the parts books.
  

The XLCH upper (welded on) oil tank bracket is easily spotted.

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66-69 XLCH regulator mounting tabs on left seat post.
67-69 (only) 2-point wiring terminal installed on the left seat post boss with two screws below the regulator tabs.

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