Yeah that backspace is pretty limiting, as to selections.
That's why I narrowed my rear, and just tucked the springs in about 3/4 inch. Now I can use 4.5 inch bs, and have a whole world of non-custom aftermarket wheels to choose from. The money I spent on the narrowing I saved in being able to use the wheels I already owned. Back in 99,(I don't know about today), 4.5bs was a very common bs..
I remember in about 1972, trying to put wide tires under my 1970 swinger. It was a problem then too. G's was the biggest; which translates to 8.25 tread width, which, in radial-ese might be 255s.
By moving the springs in just the 3/4 inch, that the offset kit provides, adds about 19mm, so 275's is where it's gonna top out at, using tires down to 50 series. And I think blu already mentioned that.
275s will like an 8.5inch rim for long tread-life and to run a decent pressure. 8.0 minimum.
IMO, 275s look pretty good, especially 275/60s. There are only a few manufacturers of street 275/60s out there, and the ones I tried, both got easier to spin as they age. By the second summer a sharp teener can boil them pretty good.But they continue to look good for at least two more summers,lol. I took 'em off and put them under my slanty car. With 2.45s the 225 couldn't even squawk 'em,lol. But the ol' Volare looked pretty mean