I have a 528 MP crate engine. I understand that basically, this block is at max bore? I just assumed that any new block was capable of being overbored at least once(pending sonic check) but is Ma using the same mega block as the 426 and max boring it?

It's the siamesed block they use and they are sonic checked before they take them 4.50". I'm quite sure you could over bore it the next size but sonic check it anyway to make sure. With a 4.80 bore center you don't have much between cylinders so I wouldn't go anymore than what is nessasary to clean it up. Dave