[Brian]

press on gear; I once encountered a 'slipped' cam gear...To fix it in place I aligned the timing marks; crank and cam gears, and made up a shaft with a tang on the end of it [to duplicate the tang on the distributor] I inserted the tang into the slot on end of camshaft and rotated camshaft until its timing mark aligned with that on the gear. [Remove sparkplugs first to enable this...] Then, to prevent the gear from ever slipping again, I drill and tap a couple of 'scotch keys'. These are simply grub screws fitting exactly on the seam of camshaft snout and camgear, which prevent any subsequent movement between the two.
Actually, I now install scotch keys in ALL camshafts with press on gears [which I use exclusively- steel 32 cams], in every engine I build.