Might want to look for a broken valve spring/springs, bent push rods or broken rocker arms. Some of these migh be a giveaway if it's running rough or has a ticking/knocking sound. Doing a compression check as Mark stated is going to tell you alot about what's going on. If you can't find anything else i would start there.
"If you can leave black marks on a straight from the time you exit a corner till the time you brake for the next turn.......
Then, you have enough horsepower."
My 67 Camaro Time Line
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