sounds like you are thinking over your head
what exactly is your goal
what is an RPM head?
340-360 heads will lower your cr as the factory did with the late 318 4bbl cars
you can mill your 360 heads or buy pistons to raise the compression back up
but what are you trying to do
what gas?
you will have to balance with new pistons
cc those heads and figure out what compression height and dome cc you need to get you where you want to be
post up the rest of your project weight, gears ,trans usage, usage, usage
