350 hp out of a fairly stock 340

Mean416 said
I don't know.

I do know that any big inch big block with good head flow can make a ton of power

What I`ve read it was a late 60s vette engine. 426 was like a $500 extra option. the 427 was several thousand option with close to 13-1 compression.
That`s a lot of coin in the late 60s