Can't open the doors!

My brother and I bought a 72 Roadrunner that's been sitting in the same spot since the early or mid 80s. The door mechanisms refuse to work. We were able to get the windows rolled down and can climb in the car. The upper door panels came off ok, so the mechanisms have now been drenched with several different kinds of penetrant. The linkages now move ok (or at least they seem to), but the door is still stuck solid.
We are at a loss as to what the next step should be. We don't want to destroy the doors, so does anybody have any ideas on how to get them working?