[Boog]

As a fellow 69 stepper owner myself I like your choice. I suggest you do a good lookover top to bottom before starting your search for parts. If it has the upper rust it surely has floor, rocker rust, etc. You may be better off to take your time and locate another cab altogether and just swap em out. Sounds like a big job but it's not really. Do as some guys like Powell 72 and drive his truck while he repairs another cab to be swapped when he's done with the cab.
Don't let the bad things you've found turn you off from this project. Hey, it's 40 years old. It's got some cancer. It's still a good start.