I have one for my T140, and ist really well made. no sprag clutch but Bendix Ernst H (germany) makes a similar set up. to go on the generator platform, but has changed the castings heavy. not fitted yet, to bussy....
To my modest opinion the originally made by Sam Manganaro (i thought so) with the HD Sportster unit is the best one, although it needs to change the underside of primary cases, and a shorter gearbox layshaft. and lower G2 plate, all good fun. oh and dont forget the decompressor, either HD solenoid with delay on ignition, or as per original. and sprocket M=2,5 with 74 fits (bit bigger as 72)
Basically all that was needed to do my Norton conversion was a starter motor and a ring gear, some steel plate, nuts and bolts.
I did purchase another set of engine plates to modify, inner and outer chaincases, an oil tank and battery box, these were so I could sort the conversion out on it's own without dismantling the bike so it is a direct replacement when I have it apart later in the year for some other major work.
The starter was £103 2nd hand off ebay and the ring gear £63 also from ebay, expect to pay more if you want a Sportster ring gear, that one was very cheap compared to others. Harley ring gears are 78t for Sportsters