340 question

I would not sweat a cast crank
and would change to cast stroker for anything short of a trailered build
small valve head is good as you can go to chevy 1.94 or 2.02 and get a new valve seat or magnum valves, anything with better shapes and lighter- lots of interchanges including +100 long for more choices in springs if you are going to run a high lift cam
(which does not work with stock heads BTW- they get turbulent)
problem is if you need ex seats and guides and valves the extra flow benefits of new heads becomes more than enticing
so let the heads be the decision maker unless you have the funds to do both the short block and the heads
heads make more difference than a small increase in compression
if you do do pistons with stock heads get the KB's that are designed for that application
skip roller rockers and other money wasters