12.0 CR is pump gas? Lots of alcohol in the gas down there? Me personally, I'd be building a 360 - probably not as rare or $$, cheaper, bigger bore, lot's of stroker kits available, won't have to build it as radical as the 340. But..most should go .060 but get it sonic checked. 12.0 will need head studs and really good gaskets - 4 bolts per cylinder can lead to sealing issues. Years ago guys o-ringed those blocks, nowadays Cometic might make a head gasket to handle it. May need oiling mods too, if you are looking to turn some RPM. The MP/DC Engine manuals are your friend.