Passenger Side Heater/Vent Door Question

I hope this is the correct forum for this question. I am rebuilding the non-A/C heater box in my 71 Dart project. The passenger side door in the box won't move and it broke out the lower corner of the fiberglass in the box. I have repaired the broken out rivet hole, but still have to deal with freeing up the hinge point. I believe that it has rusted tight, although there is no visible rust, but the rivets used in the hinge point are really tight. So tight that the little lip around the perimeter of the door tore near the hinge. What have you guys done to successfully loosen up or modify this hinge point to return the door to usability? I have thought about removing the rivets and replacing them with small machine screws, but there is not a lot of room there for that. Any suggestions are appreciated! Thanks in advance!

Jim