a gap at the bottom . i would think means a sag in the center of the cab .the wood door post could be shot.
i put my 36 on a s-10 frame had to pull it along the door (front to back)and across the cab(left side to right side) on the inside, to get the door to cab lines .. rachet straps are my freind.
after i got my lines i made frame work of 1 1/4 sqaure tubing to hold it all in place.
hope this helps