Wrong heads for a 273

It all depends on what you are doing with your 273.

Oh yeah, I agree. If it was mine, I would TRY to put it together so there were no big cuts on anything. That way you wouldn't have any bastard parts. I would use either the 302 castings or the 5.2 Magnum castings if I was doing one......but I'm not so it's kinda a moot point.