The rears are 15x8.5 with 275/60/15 BFG Comp TA's on them, but the backspacing is incorrect for an E-body, and they don't fit well because under a large bump the quarter panel may hit the outside of the tire, and they are also too close to the leaf springs.
I recommend 15x8 Centerline Terminator Auto Drag III's, which have the recommended 4.5" backspacing. I know this would fit your car perfectly.
I hope this helps.