The old dude next door used to be an amc freak, he has been cleaning out all kinds of parts and such and let me grab pretty much whatever I wanted. I want to change my yj engine someday so I grabbed a 401 block. The problem is that the bore is 3.75" but from what I've read it should be 4.165". The block clearly says 401 in 2 different spots. The only other mark is what looks like an x or a + maybe. Is the 401 a casting reference and this is something smaller? If so, what?