1975 was a bad year for valves (and pistons)
lets get a 30 year old engine and stick some boost in it. that'll work. NOT!

and a bigger oil pump wont stop it detonating its ass out (but helps the crank live(and empty the sump faster, but thats another issue) but that doesnt seem to be your problem)

but seriously is there enough piston to see if the ring lands are smashed? going by what i can see in your pics either the ex valve failed or the engine detonated the piston ring lands out and then seized smashing the piston