Wheel and drag radial questions

[68GMCCustom]

I'm getting ready to purchase some 10" wide 15" truck rallys and MT ET Drag Radials and wanted some feedback on the rear wheel backspacing and tire size. I'm unsure if I should get the rears in 4.5" backspace or 5" backspace? The wheels this truck had on when I bought it were 16's and it had the '68 Dana44 in....they rubbed the inside on turns, etc.
I was planning to buy 315 or so wide rear drag radials...but now see theres a TX drag racing series that limits rear size to a 275... or 28x10.5. The truck will get a different staggered combo later on in its life (when repainted)....like 17x8 fronts and 18x10 rears...which would probably take it up to a 30" rear. The truck does have a rear fuel tank to put more weight over the tires...but it doesn't seem to help.



So.....with a truck and the way this thing spins 275's on the street (1st can't grab and neither can 2nd until over 1/2 way thru its range) I'm afraid a 275/60-15 drag radial isn't going to be enough. I had planned on a 315/50-15 or even going up to a 30" tire with a 315/60-15 and lowering my rear gears from 3.73 to a 4.10 or even 4.56.
28" tall rear tires would avert the extra rear end expense tho.




So guys, help me out with your opinion.......4.5" or 5" b.s. for the 10" rears? Truck is a '68 short/step side and now has a '72 12 bolt.

And.......315 rears? or 275 rears to keep from being disqualified in some series? Or is this series a rare thing and just go with the biggest I can get to assure no traction issues? (315's?) And....stick with the 28"s? or make the move to 30"s now. I'm not even sure what class this thing would go under...other then just running a bracket series. On paper....truck should run 12's or so (or better).