I have a 56 Fairlane Town Sedan with a stock Ford 3.89 ratio rear end. I am running custom 5" backspaced Cragar 15"x8" rims with P255/60R15 T rated Dunlop G/T Qualifier 27" diameter tires with an 8.2" tread width. I had to replace all my leaf spring bushings, fabricate a panhard rod and trim off some frame protrusions in order to keep the rear end sufficiently centered to avoid tire scrub when turning. My 56 original equipment tire diameter was 27.5". The tires are big enough that I have to jack the car as high as the jack will go to wiggle the tire out of the wheel well. Carry some good tire chocks in your trunk for changing a tire if you go this far.
If I fine tuned the wheel backspacing more, went to a better Watt's link rear centering design and limited axle vertical travel, I could probably stuff a pair of Mickey Thompson ET Street 27x10.5x15LT tires under my ride. But, I'd likely need a way to undue the axle drop restriction to change them.
My spreadsheet of Joe Pettit's chassis tuning model calculates 354 ft-lbs of engine torque to break my right rear Dunlop radial tire loose (3.89 ratio rear end, 2.49 ratio 1st gear and 0.8 radial tire friction coefficient). With my traction bars and current 322 cubic inch y-block tune, I have all the traction I need without ET Streets.
Jerome