I believe most of the time, the best place for the cab is on the frame if it's going to be cut on. The cab-to-frame mounts will help keep the correct geometry and will assure the cab fits. Be careful of what you are doing and the reason. Also, in limited space, you are creating two big pieces. Then you have to have a way to move the cab around.
But, of course, we don't know what all you are trying to fix yet. Still waiting for that info. (minor or major)(structural or cosmetic)
The good news is that yours is a 1960. More rigid construction. Better designed box than earlier years.
