Some overheating problems...

[70 Cam Guy]

Unless I'm misunderstanding something here, it's possible your head is cracked, but it's also quite possible you've just blown the head gasket. I wouldn't write off the head before knowing for sure there's a crack. And even then, some cracks can apparently be welded closed.

I definitely agree. If you've got premix (the green/brown mayonnaise), I would pull the head and have machine shop inspect it and pressure test if it's not toast.

Incidently, there always seems to be one or two heads appearing on Cragislist. Buyer beware if you're not absolutely sure what to keep an eye on, or pay to have it pressure tested/inspected by a pro. I have seen heads on CL for 100-300 locally

[Orangys280Z]

If you're running the stock 74 head, you might want to look into one of the better flowing ones (larger valves) from the later Z years.

I'm running the stock 77 head right now(N47). Hopefully soon I can take my Z to UTI and have some of the students there check it out for me(I'm in basic electrical right now so I have to hand it over to some other students). I'm hpoing its simply just the gasket. But with my luck, it probably will be the head itself. hahaha