I would bore out the pulley and broach it for a key. Also drill and tap above the keyway for a grub screw. I would because ive just done it for 4 pulleys for nema 34s.
The only problem I had was that I bought a spare nema 34 a while ago just in case I needed one. All bought from zap and all have the same part numbers. The only difference was that the new one has a smaller shaft diameter than the older ones. No prizes for guessing which shaft I measured before I made the broaching socket, drilled the pulleys and cut the keyways.
Ah well at least a smaller hole can be bored out.