what has to me moved/sectioned to lay frame?

i'm just about to airbag my 91 standard cab fullsize 1500 chev and was wondering if anything has to be moved or sectioned? mainly and crossmembers or if the fuel tank has to be raised or if it must be sectioned? i know i will have to tub the front but in the back how tall of tire can you run in the factory wheel well?

im runnin a 245/35/20 all the way around, had to tub the front and rear,still need to raise my gas tank up like an inch...you dont have to notch any cross members

the inner fenderwells front and rear will be in the way, the gas tank will touch the ground, the transmission xmember bolts will too, the exhaust crossover pipe is in the way, wiring harness on the driver side, battery on the passenger side. wiper fluid container, and over flow container. if you run the stock 235/75 tires you can hit the firewall back where it touches, but if you are runnin 22s the same size as the stocks, you'll need to tub it.