Valve guide boss cracked

Correct on all counts! “If it doesn’t migrate” is a gamble I don’t like taking either. However, the cracks through the seats between the valves of 302/308 heads are a prime example here. Those make me even more nervous but a pressure test it the go/no-go gauge for those. It’s rare for them to fail once they stop migrating in most cases because your just not pushing the casting to its limit. Now start adding in things like race gas compression, triple valvesprings with dampers, etc. etc. Well, you’re throwing good money after bad because you will get more with a good set of aftermarket heads to start with for the same amount and not be pushing everything as hard.