I forgot to mention I dont really have a "stock" setup. It has a 69.5-72 b-body rear with a 3.54 powr-lokr. I think it is slightly narrower than an e-rear? I know the mount pads were modified by the prior owner. From the old welds it looks like the pads were moved outward almost an inch on each side.
Anyways, I do know I have 275/60-15s in back and I have about 3/4" clearance from the spring right now, with about a 3.5" backspace on 8" rims, so maybe a 4" backspace would be about max.
Hmm.
Not sure about the housing width. In B bodies, 66-67 are the narrowest, then 68-70, then 71-74. I think stock E body housings are wider still. In an E body with a 10" rims, a 66-67 rear can use 5" back space. With 68-70 rears you need 5.5 backspace. With a 71-74 rear, I dont know. Also , have your springs been moved at all?
I have 295/50 tires on a 8" wide rim with 4.75 of backspace and the stock spring lcoation and housing. My tires are about .25" away from the rear spring segment and about 1.5" off the wheel opening lip.
I recently read a big tire test about 17" performance rubber. BFG had its butt handed to them. I think the overall best wet/dry, handling and braking winner was a Kumho or Nitto. Price was also a facotr in this as they figured they were testingmid range tires with a price cap of $150 each. The one unlimited tire they threw in for validation was a Michelin Pilot. While it did pretty good overall, it actually was beaten in a few catagories and was priced at well over $250. They got all the tires from Tire Rack and the test was conducted by Car & Driver, so there may be a link on either of their web sites if you want to search it.