47-55.1 Two Steps back. My high school chevy 1950 3100

[dsraven]

when i did a firewall in a task force truck I used 16 ga sheet and had a fab shop do the bend. I started by hanging the doors with a good set of hinges, fit the door to the opening, then installed the latch plate and adjusted that so the door fit well. then, with the doors closed I went inside and tacked a length of 3/4 black pipe across the lower part of the opening, about 4" off the floor from the front to the rear of the opening. then a cross brace from the rear of that pipe up to the top corner of the door. then I ran an X of pipe from the lower corner on one side to the upper corner on the other side behind the firewall area to keep the front of the cab from becoming a parallelgram. do this after a few dimension checks to ensure it isn't already out of shape. then I took the doors off. the horizontal pipe above the floor allows a long 2x4 to be slid under the black pipe and through to the other side so the cab can be hung on a set of sawhorses by the 2x4's. I also braced the back of that cab but that was becuase I removed the whole floor, firewall and rear wall. I made tacks that can be ground off with a zip disc but will be strong enough to not come off while working.
I have used self tapping sheet metal screws before with success as well. a hole is a hole so even a cleco needs a spot weld when done.
when you hang the doors first there is a good chance they will fit properly when you go to install them again. lots of times I drill a small hole through both parts when they are adjusted right, mark the hinges whare they go etc, then when they go together for the last time they usually fit well.
weld through primer is a copper or zinc product that conducts the current. regular epoxy or other products may not. a tip, when you use a mig always cut the wire before you start so there is a chisel tip on the wire that strikes a spark right away and doesn't leave a bunch of contaminants in the weld from the oxidized ball that is usually left on the mig wire from the last weld.