Welcome Brian!
Yeah, post up some pics
The door issue sounds like worn out hinge pin bushings. With the door open, try lifting up on the latch end. If the bushings are worn, you'll be able to feel the door wobble up/down a bit on the hinges. Replacing the pins & bushings usually fixes the problem.
Also check the striker bolts in the door jambs. They have a built-in plastic bushing that often wears out and makes the doors hard to close without slamming.
The tank selector valve for this year is a simple 1-wire hookup. All the other wires in the dual tank harness go to the gauge/sending units. The wire is green if I remember correctly. To run off the main tank, no power is applied to that wire. When you switch to the auxillary tank, power from a jumper that plugs into the fuse box is fed (through the dash switch) to the green wire leading to the solenoid valve. Use a test light on that wire to see if the dash switch & associated wiring is okay. Also make sure the solenoid valve is securely bolted to the frame and that the connection is free of dirt/rust since that's the solenoid's ground connection.
The ID stamping on some big blocks is on a pad above the timing chain cover (instead of on the pad in front of the pass side cyl head).
Q-jet carbs have a lockout mechanism that keeps the secondaries from opening up while the engine is still cold. It's tied into the choke mechanism. So make sure the choke is opening all the way and not sticking.
The secondary throttle plates are hooked via a linkage rod to the primaries. Unless the lockout mechanism is holding them, they will always open (even with the engine off). However, the secondary air doors (up on top of the carb) only open based on airflow demand. Just reving the engine up (no load) won't make them open. You should be able to push the secondary air doors open by hand though (against slight spring tension) ... if not, check for something that's binding/sticking.
The grabbing rear brakes could be due to a leaking wheel cylinder or axle seal that's contaminating the brake shoes with brake fluid or gear oil. If I remember correctly, the wheel studs are pressed through the brake drum, then through the hub, connecting the two together. So to remove the drum/hub assembly, you have to unbolt and slide out the axle shaft. Then remove the snap ring, key, and nut. That'll allow you to pull the whole drum/hub assembly.