340 stroker build questions

Your best bet is not to buy until you have a plan, and the best idea for a plan is to work with your machinist.
As for my opinion - I'd run the RPMs, checked and corrected, a dished piston, stud the mains, blueprint the block, and run either a hydraulic or solid flat tappet around 240° duration @ .050 for the 425hp goal, and another 250°-260° duration @ .050 if you want more. If you plan to turbo it, plan at that time to change the camshaft too.