Time for new tires and rims for the 68 Dart

The same tires and rims are on the car since I bought it in 2012. Fronts are 15 x 6 w/ 4.0 back space steelies shod with 205/60-15 BFG. Rears are 15 x 7 w/ 4.25 back space steelies on 245/60-15 BFG. The tires are embarrassingly old and as much as I dig the steelies, I've (pretty much) decided on Torq Thrust D's, VN105. The rear tires rub the inside lip of the quarter slightly when hitting the curves aggressively. The fronts have no fitment issues.
It's been years since I picked out tires and rims and after searching and reading dozens of threads in this forum plus scrolling through scores of online sites, I now know how much I don't know about choosing tires and rims.
I think the front is sorted out: I'm staying with a 15 x 6 rim and a 205/60 or 65. Tire will probably be either a Cooper Cobra or BFG again.
The rear is where I have questions. I've done extensive measuring and in addition to the 4.25" bs, laying a flat edge across the back sidewall, it's 5.25" bs. Measuring from the face of the drum to the edge of the spring is 6.25". That gives me 1" of wiggle room, verified by the photo below. So I'm thinking I'm golden, all I need is a rim with 4.75" bs. The problem is that the 7" TT only come standard with a 3.76" bs. Up until just recently I assumed wheel manufacturers made their popular rim sizes with multiple bs' for people to choose.
Now I understand why a lot of members decided to go up to 17" and 18" rims. But I want to stay with 15s, so the obvious answer is have American Racing make me a custom offset. Is it common for people to request custom offsets? Or is it more popular to stay with standard offset and roll the lip? The problem is that with a 3.76" bs rolling the lip isn't going to help. To further complicate things, I want to go with new MT ET's 255/60-15, which have a section width of 10.1, about 1/3" wider than my BFG's.
Any suggestions, or is there something I'm overlooking?

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