Rear End

Since you have a Duster, I would start looking for a 65-67 or 68-70 B body 8-3/4. Those rear ends are wider than the original A-body 8 3/4, but the Duster has much wider quarters than the Darts did anyway. The B-body 8 3/4's are cheaper, easier to find, and had the large bolt pattern from the factory. All they require for installation is relocating the spring perches, which is a pretty simple operation. While you're at it, you can set the perches up to use a 1/2" spring hanger/shackle offset from Dr. Diff, or a full 3" spring relocation so you can mini-tub the car for some really wide tires.

My Duster has a 68-70 B body 8 3/4, uses a 1/2" spring hanger/shackle offset (perches are 42" c-c now), and still has the stock wheel tubs. I run 18x10" rims with a 7" backspace and fit 295/35/18's on the car after a little quarter lip trimming.