I picked up a set of 308 heads off a 360 down at the semi-local pick-a-part, haven't even got them de-greased yet. I've seen some traffic about crack problems with these heads. Where are they most likely to crack, and how critical is a crack that's not leaking water on a 308 head set up on a 360 street engine running 9:1 compression? I'm only out $40 for the pair. but it took me forever to find a set and I want to use them if possible. Thanks.