when i talk about top end i mean 5th 6th, i do a quarter mile and 8th of a mile asphalt and on a 350 we usually run a 16 39 ,16 40, for the quarter , and yea you could get that stock cylinder to put out 80 hp i got my stock crank 50 over but with every trick on the book doing about 75 hp , a 4mm stock cylinder 68mm full drag port job with cpis and carbs should do about 80 hp. but yea your easy way out is a 4mm cub .