The recommended wheel sizes for e-bodies is 15 x 7 front with a 4 1/4 backspace and 15 x 8 rear with a 4 1/2 backspace, For each additional inch of width you want an additional 1/2 inch of backspace to center the wheel. If the rear end is centered, which they seldom are, you can fudge a little. Remember, too much backspace can be overcome with thin spacers, but you basically are stuck if you have too little backspace. The dimensions are the same no matter how large the diameter of the wheel. Unfortunately, the non speacial order wheels are usually only available in even 1/2" increments. A good tire store may have the device needed to measure your backspace. They choose the tire size first and mount it in the device and move it in and out to where it's centered and then read the backspace needed on the index. If you special order wheels from any manufacturer...they're yours, no matter what. Good luck. P.S. The larger the wheel, the rougher the ride and e-bodies have enough cowl shake as it is. If you install urethane bushings, large wheels and sub frame connectors, you may want to invest in dental insurance since it will definitely rattle your teeth. That's why I stayed with 16" wheels on my wife's 73 Cuda and stock 15" rallyes on my 71.
By the way...you can get Boyd Coddington Smoothies which look a lot like TTII's and they're $250.00 each at Wheel Vintiques. Check out their website.
