There are small backer plates on the cams that I still have around. Nothing large enough to drill and tap for adjustment bolts though. You'd have to machine off the old one unless there's room to just weld the new one onto the backside in halves or something. You'd have to be really careful about getting the gear aligned back up correctly, or it would change the lash clearance and chain alignment... Looks fairly easy if someone knows a good machine shop...
