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.

You got em cheap enough...drop them off at the machine shop for a check.

Those cracks are almost certainly not the reason that truck went to the junk yard. If they are not into the water jacket, I would run them and not loose any sleep. Guesses are that lean fuel mixes on emissions engines made cylinder temps high enough for cracking. On a performance application, you'll probably have a richer mix and maybe a little lower cylinder temps. So on your engine they may not be as likely to crack.

I left mine at the machine shop, they normally crack in-between the 2 valves on the end chambers, i'm sure mine were toast, the crack went down on each side about 3/4", also found cracks on the other head, so i junked them. On the 1 chamber that was really bad, showed signs of pitting on the valve & seat, so i'm sure coolant was getting in.

Most machine shops i've called are very familiar with the cracking issues on these heads & don't want to mess with them IF there cracked, your just rolling the dice whether they will leak or not, thats if the machinest doesn't want to jack with them & you just throw them on "AS IS".