Front Rubbing - Tires, Suspension or Wheels?

In the front with a 17" wheel you can go up to about 5.6" of backspace. With that amount of backspace you should be able to fit a 255, a 245/45/17 won't be a problem at all.

On an A body you can fit a 275 wide tire in the front, with 73+ BBP disks it requires a little over 6" of backspace on a 9" wide rim to be safe. That requires an 18" diameter rim though, because most 17" rims hit the outer tie rod around 5.6" of backspace.

The issue with your current wheels rubbing is the backspace on the wheels. 3.375" of backspace isn't nearly enough. I have 225/60/15's on my Duster at the moment, with 4.25" of backspace on 15x7's. I have no rubbing issues whatsoever. I will soon have 255/40/18's or 275/35/18's on 18x9" rims up front with 6.4" backspace. It'll have 13" Dr Diff rotors though, so that's an extra 3/16" on the track width, so effective backspace compared to a factory BBP disk car will be about 6.2".

I know both tires will fit, I just have to decide how much tire my arms can handle with the 16:1 manual steering box. :D

In the back with a stock A body rear and a spring offset you should be able to fit 275's without issue. Again, you'll need a 9" or 9.5" wide wheel. For backspace you'll need 4.75" to 5", 5" for sure on a 9.5" wide wheel. I wouldn't go more than 5.25" of backspace in the rear with the stock rear end, you'd probably need a small spacer at that point. 17 or 18" diameter doesn't matter except for tire selection, the springs and the quarters are all you have to worry about.