If I can't find a good replacement cab I will be replacing mine, along with the floor, cab corners, rockers.....
That would be the best thing to do and keep most of the things together untill reassembly.
I replaces floors, cab supports, rockers, and bought piller patch panals on a 68 GMC cab and it was alot of work. The hardest thing is to keep your door gaps when welding it back together.
