I saw where you asked this on the FordFE.com site. I too plan on using a 4.25 Scat cast crank in my 390 block, but my motor is already .060" over and I think I can go another .020" to take it to the stock 4.28 bore and still have .125" wall left barring core shift. I finally found a place to sonic check a block that doesn't charge an arm and a leg. $90 for a 12 point check in all 8 cylinders. I plan on grouting the block to the water pump holes anyway as it'll be a drag only motor.