Yes, to summarize: you need a 3/4" bore clutch body (the fixed outer housing with cork lining) to mount on your Briggs engine crankshaft, and an alloy version is the practical choice since cast iron is scarce. Your existing iron inner cone on the( PTO shaft ,12 in image) pairs perfectly with it.
A 3/4" alloy clutch body (lots of online stores sell them) fits directly on the crank with matching keyway and grub screws, engaging reliably with the iron cone via cork friction—no metal contact issues arise.
The alloy body is lighter than cast iron, but the difference is minor for SB45 mowing: a lot of the inertia comes from the iron cone, reel, chains, and gearbox. Users report no noticeable effect on cut quality, drive smoothness, or engagement once adjusted—many Briggs conversions run this setup for years.
I think I saw a a 3/4" bore clutch body for $110 new.
