This conversion information provided by 'dave76' of the XLForum - http://xlforum.net/forums/showthread.php?t=2082025

I finally found time to finish this project on my 1990 1200 XLH Sportster. I took it for a ride afterwards (it was freezing weather - but I enjoyed it). The belt is definitely quieter and smoother than the chain configuration.

I found multiple used rear pulleys on eBay under $50. I got a used but perfect 128 tooth belt for $65.
I got the belt guard for $35. Only bought a new VTwin front pulley for $85.

Top: Belt guard ———- Bottom: 4 speed chain guard

A standard 1991 Belt Drive Sprocket Cover will be needed. The left middle bolt will not be used so I just placed a short faux bolt and nut there.

The Belt I used was 1-1/8“ wide with 128 teeth. This puts the axle adjuster in the middle of the range.

The main part numbers that I was able to find were:

40271-89 – Front drive pulley 27 tooth

40258-89 – Rear driven pulley (pulley only not the chrome guide cover).

40273-89 – Rear pulley chrome guide cover.

I cannot find the number for the top or bottom belt guards. I sourced my rear pulley off eBay, the front came from V-Twin (Taiwan teddy).

40022-91 – Drive Belt (Standard Harley 1-1/8 x 128 teeth).

I bought the counterbore from eBay. This is needed to sink one of the case bolts about 3/16 of an inch to provide better belt clearance.

To clear the new belt drive sprocket, I used a 1991-up Drive Sprocket Cover. On the engine, the top rear stand-off stud (near the motor mount) needs to removed. It is replaced with a 7/16-14 x 2” bolt. The unused (open) hole in the sprocket cover just gets a faux bolt and nut.