I don't see how a load of bad gas could cause all that mechanical damage. I think you had two scenarios going on. The things that would cause the damage you've outlined are like Mike said, floating the valves, or some other mechanical interference like coil bind, insufficient retainer to guide boss clearance, insufficient rocker to stud travel, insufficient valve to piston clearance or the cam going soft. Something had to give in order to provide the clearance to allow the rocker to move off the pushrod.

If this was my motor, I'd disassemble it completely, mic the lobes and clean all the garbage out of it. If I was a bettin' man, I'd bet on a soft cam.