Rear end housing width question

I'd go with the shortest backspacing possible in the wheels you want, then measure for the rearend so it works with those wheels and tires. This will make it easier to take the wheels on and off. Plus, it saves a tiny bit of weight, though not much. I've got 15 x 10" wheels (4.5" BS) with 315/60/15 drag radials on my '66 Dart and it's a pain in the *** taking the wheels on and off. If they had 3.5" backspacing, it would make a world of difference.