All hardened seat heads are prone to cracking from the mid '70s to now. Iron cracks, aluminum warps.
I would skip over them every time for something that's supposed to make power, especially if money had to be spent. My running them- it was more worthwhile having lower CR. Motor woulda been pretty decent had I put 360 heads on it. Might they be worthwhile? Sure. But if you're gonna run 318 heads there isn't really much difference in them. In stock form none are very good or better than each other. A better cam and converter would be a much more worthwhile investment than machining 302s.
The smog 360 heads do almost the same job of supporting power as the pre-smog 360/340 heads and the 308s excel in some areas. But those were larger port heads than the 302s that were more meant to be ported and run.
Cars, trucks, vans, don't matter- '85+ 318s had 302s unless they had 360 heads. Trucks, vans got flat tappets before TBI though.