What about getting a large steel bar or tube, somewhere in the neighborhood of 2 x4 or 4x6, add a large c-clamp. Remove the hinged door/window, using the bar/tube and the c-clamp try to get the dent to come back out. I would think that it would be worth a try. Otherwise, you'll have to get busy punching and drilling.
95 IH 72 passenger transit school bus w/ DT466 and 545 Allison.
79 IH Scout II/392 (0.030 over) Hamilton Injected/727/D300/Full size axles/36" Swampers/Lockers/OBA/38 gal Custom fuel tank, roll bar, tube doors.