ok, on the banner your car have 15x7, but they look wide because they have biggest offset.
I have stock 15x7 and they are really more inside the fenders.
I found also stock 15x6 from a diesel caprice, I will cut them and add 3" at the exterior rim.
I think I will be correct with 15x9 on 4 wheels, with 245/60R15 (or 255/70R15) on rear and 235/70R15 on front,sand blasted and glossy black, white letters tires and chrome dog dish.
I hope they will have enough clearance.
also I have a stock ring and pignon for gm 10 bolts taken from a blazer k5, 3.5x/1, will it be better than the stock 2.5x/1 and will be street driveable behind a th350c ?