Back in my tractor pullin' days I had a 468 built with a truck block and .400" long rods. That thing lasted forever w/ a 10-71 on alky. Finally had to retire it when the deck was full of heli-coils, no water leaks 'cause it was filled to the top. I suppose you could go .100" or MAYBE .125" over, but better check for core shift and wall thickness to be sure. There is a reason the aftermarket blocks are so good..... 8) JB