re: I may be in the market for an F-250 over the next few months

The emission control equipment is part of the motor, so it is the motor.

Blowing head gaskets doesn't have anything to do with emission control equipment. It's a junk motor. Anything you have to put $4k in to make it reliable is junk. The 6.4 is worse. It was built to hold Ford over to the 6.7 and not do anything more than that. Absolutely no way I'd buy either one of them. I would be less scared of a 6.0 if I knew who owned it and how they used it. I wouldn't buy a 6.4 unless it was so cheap that I could drive it home and sell it for a good profit.