If I understand correctly, after the initial run many McCoy's were assembled by prople who did not understand engine fits and you sometimes got a good one and sometimes a bad one. This was during the time that they were offered at "fire sale" prices.
I have two .35's that have excellent compression. Bought them used, not sure when they were made.
According to GMA, one of the short-life factors for many was the Testors 39 fuel. It had insufficient lube. I am guilty of using that fuel too. who knew, we were trusting folks back then.
The "lightning bolt" version was an improved model...bronze crankshaft bearing, etc.

George