I run 275/60/15's in the back of my 88 wagon and
255/70/15 up front, both mounted on 15x8 truck rally rims. Front barely rubs when parking, the rears are great!
I'm not a 100% sure but I believe that the 77-90 wagon rear ends are the same width as the bubble sedans and wagons. I still have more room in the rear to go wider.
With my 4.10's, trutrac, Hotchkiss rear arms and 2400 stall, I get a 1.96 60ft time with 38-39psi in the tires.
I run the Cooper Cobras and I love em. Great at the track, on the road and amazing in the snow. And they stand up to a LOT of burnouts!
I'm actually bracing up a frame I picked up from a junk yard and I'm looking for and good mods to beef up the frame.
HELPFULL HINT
I found a lot of ideas for frame bracing on the b body's from looking at what guys did do their g body's and a body's.
The frames are similar, just smaller, but close enough to use the a and g body designs to make my own braces