Ok.......I got a friend with a 1990 4.9L that he picked up about a month ago for next to nothing with what we thought was just a blown head gasket. About 2 weeks ago we pulled the head off of it and its sat since. Since then the head has apparently rusted and a crack as become visible in the head. Anyway he talked to the machine shop and the machine shop told him the 1990 4.9L is apparently notorious for cracking heads. They want to sell him a new one at like $550. Yes I understand he's gonna need another head, but is what this machine shop told him about the 1990 heads cracking TOTAL BS or not? Am I correct in the assumption that all 87-96 EFI 4.9L heads are the same and completely interchangeable. Any help will be appreciated