Well, here's my two cents worth:
I don't have big bucks, so I could never do a frame off restoration. I HAVE to figure a way to repair it without doing so. I would never take the cab off the frame until I had all my welding and patching done. The frame is your foundation...park it level and keep the cab sitting on it while you patch it. Don't take the doors off either...until you get structural rigidity again. Leave 'em on so you can keep an eye on warpage and stress. I've read horror stories from guys on this board that their doors no longer fit after welding everything up. I'd also serioulsly consider welding temporary braces between the door frames to keep things from moving whilst cutting and welding. I would keep as much original metal as possible especially where the footwell meets the firewall and kick panels. Consider buying flat sheet stock and making a few small patches rather than huge Chinese-stamped panels that aren't just right anyway. That way, you know your original geometry is maintained. Then, when everything is solid again, take the cab off and blast it. You won't have to worry whether or not it's gonna fit when you get all that pretty paint back on it...you'll KNOW.
Jim
