What rear housing is in your car?
Yes, typically moving the springs in allows a wider wheel, however you are still limited by the wheel housing on absolute size of the tire in regards to width and height and the rear end housing will determine what backspace your wheel will need.
For example, with the stock E body housing, you may need 6", with a 68-70 B housing you would need 5", or a 66-67 housing you may need 5.5"
I run a 12" wide tire on a 10" rim under my Challenger with room on both sides, but it is the result of careful measurement and the considerations above. You also want to check both sides of the car as sometimes it different side to side.