273/318 Heads

66fs said
Those are early closed chamber heads. I would not mess them up.

Plymouth 65 said
X heads are large port open chamber, what you have there are early small port closed chamber heads. I'd practice on something else. 65'

I dont have anything to practice on... these are just some I found for sale locally and thought they would be better to mess up than my Xheads.

I dont know what open vs closed ports/chambers means, ill have to do some reading on them apparently.