I've done the TBI to carb swap on two vehicles. A '91 Camaro 305 and a '91 Bravada 4.3 that I jammed a 350 into. It's very straightforward. The two things you need to be concerned with are fuel delivery and the throttle valve (TV, "kickdown") cable for your 700R4 if you have one. QJets already have the proper geometry on the throttle linkage for that cable. Holleys and Eddie/AFB carbs need an adapter bracket. You'll look at it and think you can make it work, but the cable needs to be fully out at WOT and just far enough out to not have any slack in it at idle. If you don't address that cable properly from the beginning, you'll be doing it later along with a transmission swap.
The other thing is fuel. In particular, fuel pressure. TBI engines don't have provisions for a mechanical fuel pump and the TBI pump puts out too much pressure for a carb. You need about 4-6 PSI but the pump puts out around 10-13. You can address that two different ways - get an inline electric pump for carb applications, or get a regulator and use the stock pump. I chose to use the stock pump both times. Holley part #12-803 will do the job. It's "T" shaped. Hook the inlet from the pump to one side of the T, carb to the other side, and the return line to the bottom of it. Put an inline fuel pressure gauge between the regulator and the carb, then you can adjust the allen screw on top of the regulator to put the pressure exactly where you want it. With the ECM gone you'll also need to provide a keyed power source to the fuel pump relay. No big deal.
I prefer that method because it doesn't put stress on an inline pump by making it suck through the unused TBI pump, (you could use the sender unit from a carbed truck I guess and get rid of that pump to do it right, but why?) the stock pump is quiet and reliable, and it's nice having an electric pump for those times when your truck's been sitting for a while. You don't have to turn the engine over and over while patting the gas waiting for the bowls to fill, etc...
The other stuff you'll need for the conversion you probably already know... Carb intake manifold, HEI distributor, throttle return spring and bracket. Might as well get rid of the AIR pump, all of its plumbing and the tubes for it in the exhaust manifolds too.
