Have you done a compression test on the engine? If your compression's good, it's possible things are just dirty.
But, if you do pull the head, your best bet is to take it to a competent shop that works on heads and have them go over it. They have the specialty tools to measure everything to be sure its all in spec and can give you a much more detailed list of what needs to be worked on.
Although, like F-250 said, if you put a freshly rebuilt head onto a tired engine, the extra compression can cause aging rings to go out.
I was in the same boat w\ my 66 240 . I was burning alittle oil , and found all my valve guide seals lying in the head gullies. I did my own valve job with a drill like my daddy showed me, replaced the valve guide seals, and the truck runs better than it ever did. I put a new oil and fuel pump on it also those 240 lower ends will run forever.