Rebuilding the frame is an honorable quest, and to an extent, doable. Replicating the original is always best. How will you mill out the seal groove to place your door seals? What I am looking at, is a situation that will require a new door as well, as it appears this one has been rode hard and put up wet, so to speak.
Would you not benefit from replacing the entire door with a pre hung unit?
Would you not benefit from replacing the entire door with a pre hung unit?