Tubbing

IMHO I would not tub it. I fit a 275/60r15 drag radial in my 70 Dart rear tub with a little massaging. I have run 10s with this set up and 60 foot times in the 1.50 range. There is more to hooking up than just large rear tires. I would work the front suspension and get the ride height leveled out to get the center of gravity. The way to get a car to hook is weight based. A good traction aid like the caltrac system and good shocks.