Well, you'll know in a hurry when you yank the heads, bench them and pour some kerosene, lighter fluid or paint thinner down an exhaust port or two. Ditto for a few intake ports. Bet the exhausts leak about as fast as you can pour.
Btw, this is why many of us here often recommend a leak-down test as well. Aside from telling if the valves, seats etc. are bad, the two tests (leak-d and compression) may prove that the rings, ring lands and pistons are still good allowing you to skip a total teardown for now.
Funny cause I do remember a local fellow who was pretty good with cars but kinda' dumb in many ways too. He added freshly rebuilt heads to an engine that really needed a ring job if not a total overhaul. Well, it ran better but man that partially refreshed engine blew oil everywhere, in large quantities, out the breathers, exhaust pipes and more! The dipstick was literally blown up off it's seat about 6" every time he hit the throttle! Gene Saubert, R.I.P.!
