I think you probably had 2 separate problems. A bad fiber gear which has a life expectancy of less than 50 years and stale gas that caused a valve to stick. I would put the new gear on whichever way you choose to do it, pull all the push rods, inspect them and replace the bent ones. I would then squirt something like Marvel Mystery oil in each cylinder and let it set about a week to dissolve the varnish. Chances are very good that will fix your vehicle. If your head gasket is good, why risk something going wrong by pulling the head.
