Paul
I've been there.
Your first task is to brace the cab in every direction possible, after confirming that the doors fit correctly.
You should probably start with the floor and cab mounts, and work your way outward. It depends on what all you're replacing (just floor, cowl, rockers, etc). You will want to make sure everything is lined up before final welding.
You can review my photos (link in my signature) and there are other resources. I'll have to see if I can find you links for them.
Good luck and keep us posted on your progress.
