I'd highly recommend the 4.25 stroke. That combination basically falls together and then you plenty of clearance for the windage tray and the internal oil pickup. Just buy a high quality 4.25 stroke crank with 2.200 rod journals and get a set of good 7.100 long BB Chevy rods and you're good to go. Most anyone should be able to make pistons for that combo, might even be a shelf piston at JE or Diamond.