The NHRA has a page with the rules. Go to NHRA.com for there guide lines. You may not need to install tubes. Move the springs inboard first. This will give a lot of tire clearance. Check out the tire threads. I do know some guys have installed 295/50/15's, 275/60/15's in the stock wheel well area with nothing more than off set shackles and/or the relocation kit that moves the springs into the frame rails.
Womenator, I love it! Nice score on a cheap and good looking ride. A low compression 440 mill running low 12's. Excellent!