I pulled heads off one of the two in order to take a look.I didn't mic it .But it seemed to measure just short of 4.5 .And if you look up a casting # 14044807 at
www.mortec.com. It lists that block as a hi-deck cnc'd 4.250 or 4.495 bore .I might be off a few tho with my tape,but not a quarter inch .This is a standard bore motor.When I get to work tomorrow I can mic ,if it matters.The one I'm keeping (the one with the heads off) is going in a 72 Chevelle .I'm doing a freshen up .More compression (pistons) and more cam ,Because I can. I won't be using a stanley tape measure at that point .