350 hp out of a fairly stock 340

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
only the zL1 was 12.5 and L88
L71 72 98 11 to 1