A 408 or 416 stroker is the best bang for the buck for 450 hp, they are based on a 340 block. I’m sure you could do any 318/340/360 and get decent horsepower, but 450 isn’t easy to get out of a 318.
not an early A body, but this is my brothers car with a 416, running low 11’s. It’s a beast on the track, and is totally street worthy as well.
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