I've worked on a couple of those. Yours looks like it's going to restore OK. During reassembly, I propped the firebox up on a 5 gallon bucket shimmed with a 2x4. Kind of redneck, but hey, that's BBQ.
Did you get the racks? I like the ones I made better. I used 3/16x1" flat stock and layed out a rectangle. Welded up then sheared out pieces of 3/4-9 expanded steel and welded it on top. They fit good, clean up well, plenty strong. A guy on this forum named swamprb has that cooker now. I've borrowed it back twice, cooks real good!
I remember welding the open seams in the firebox (on top, where the cover seals) and sanding them flat. Really helped cut down on leakage and flames burning the side of the paint on the cooking chamber.
My buddy glued gasket around the inside of the door, flat, so it sealed. Didn't make that much difference on temps, but now you don't see smoke leaking out.
I kept the grill grate holders in the firebox and made a full sized grate to hold logs. I put the grate on the lowest position. Raising it up like that really helped get better airflow underneath the fire. I also used thin firebrick and borrowed a buddy's tile saw to cut it cleanly to fit the bottom of the firebox with firebrick. That helped with the temps a lot.
If you want to cook hot and fast (350) on a Bandera, don't use the water bowl - just take it out. Else I kept water in mine. Worked great. Those are real good cookers.
Hope you got an OK deal on it. I sold my last one recently for $250. Seemed high to me but I got lots of calls (Seattle area).