I had a hard time finding a replacement drive pulley on the 5060 six speed tranny that I put in my 857. It's a 4" pulley with a 5/8" shaft and a 1/2" belt. Here's what I found and what I did to make it work, hope this might help someone else that needs one.
I found this pulley at electricmotorsite.com Part number - MA40x5/8 Description - Maska 3.95 in. OD x 5/8 in. Fixed Bore A Pulley
The hub is too thick so I turned it down, almost to the original set screw holes. Then I drilled and tapped new set screw holes at a slight angle. I left the original set screws in the holes and covered them with a little J B Weld just so they wouldn't show. In this pic you can see the original set screw hole filled with J B Weld and one of the new holes I tapped.
Here's one I made a few years ago, before I had a lathe. I just ground the hub down with a grinder then filed it the best I could. I've ran this one on my 857 for a year now with no problems.