If you are bolting the door on the mounted cab, and the door wont close, not even close, you have to find out why. Since I did a lot of work in the junkyards grabbing doors and much other goodies for sale to the vendors, it is obvious that the machinery of one plant didn't match the machinery of another. Sometimes there is nothing you can do but A) replace the doors with the doors you want from the same factory, or B) cut, modify, cut, and cut some more. If you are doing what I did and replacing the 1950 doors with 1953 doors so I could get the pushbutton and vents, even the same factory could be different in their tooling in 3 years.
Ive heard these stories so many times. Its much easier for the mild restorer, home builder, to just call Carter and get doors that fit. He has outbuildings FULL of doors. Hope this helps!