Wheel Width is an INSIDE dimension measured between the beads. Backspace is measured outside edge to mounting flange. (it's really the inside edge of the wheel from the car's standpoint)
Back in the day, the standard A-body 14" wheel was only 4-1/2" wide. Formula "S" and Dart GTS used a 5-1/2" wheel. Or, if the optional wider low profile tires were ordered (70 aspect ratio) they would come on the 5-1/2" wheel. Widest tire the factory ever put on an A-body was E70, or in today's language 195/70. A 225 would be 3 sizes bigger.
I know cars who run 225/70 on the 5-1/2" wheel (Max in CA) but that's gotta be the limit. There used to be a rule of thumb that the tread width should be within 1/2" either way of the wheel width.
If you really only have the skinny 4-1/2" wheel, I personally wouldn't go bigger than 205's. All of the A-body Rallye wheels were 5-1/2" and they are easy to pick up so you might check into that.