Before I make a mistake please help new mopar fan!!

67 383 would probably have 516 heads, they are a closed chamber with a 1.60 exhasut valve and 2.8 intake. to make good power you should at least cut the exhaust for the 1.74 valve. they dont have hardened seats. you are going to spend some decent cash on those heads to make them work. the short block came with a flat top piston way down in the hole so if you put a better set of open chamber heads on the stock shortblock, you will have extremely low compresion. like 7.0:1. if it was already rebuilt, you never know whats in it.