I did a similar thing on my 65 Cuda, 8 3/4 with 4.5 Yukon axles. I used 275 40 17's in the stock wheel wells. I had to move the rear back 5/8's of an inch and this put the tires in the center of the wheel well. To put this rubber on the car I moved the springs in, but wheel wells are stock.
Pettyblu's Dart looks nicely centerd.
I think 2.5 inches would push the rear to far back.
Thanks Keith Mopar!The 8 3/4 is from a 72 Duster and is sitting on the factory leaf pins.I have a .489 case and a 73 Dart Swinger 318 auto(904)driveshaft bolted up to the 6 cylinder (66,904)I swapped rear u-joint and bolted it in.Done.