Big Valve X Heads on Low Comp 72 340

With the addition of the 3.73 gears, headers, intake, and ignition curve would make more meaningful gains if you don't want to touch the bottom end and are looking for actual performance gains. The only way I would change the heads in the name of performance improvements is if I happened to have a set of aluminum heads ready to go. As the OP stated, though, even a low compression 340 still can run fairly good in stock form!