The id is 3/4 with a key, It came with a ton of briggs flathead parts and it fit the briggs shaft. clutch is unused but missing a bolt and spring.Looks like an axle clutch the 2 stroke guys will know .
Shaft size ?
The Burco pictured is a Briggs engine clutch, not a Burco axle clutch. No upgrades were ever made for the engine clutch. In fact, the oil clutch conversion for the axle clutch was never necessary either.Post that picture in the enduro forum there are guys running that burco that have been converted to wet clutches they might chime in and get you parts of a source for parts later Chuck.