10" on a stock 73 Duster?

I have a 69Barracuda fb which has about the same tubs as the Duster. It is lowered to be level at the rockers, with the lowest part of the K-member at 6 inches from the road. It has the offset rear spring hangers, which run about flush with inner walls of the tubs.
In this configuration, 325/50-15's on 10s still allow normal straight-line driving. But I can't corner at much over 20/25 mph as the body slides over to rub on a big old lump, that each wheel well has in it, that defys my every effort to pound it out. The lump is smooth so it's not cutting the sidewall.
But the 295/50-15s (BFGs or Cobras) on 10s do not rub, and I can drive the nuts off the car with no issues.
Interesting factoid, my 295s on 10s, IIRC, measure a tic over 13inches after mounting, which is actually 330mm, or there abouts.
The branded size on any Passenger car radial is determined on a checking rim that is 70% of the branded size; so for a 295, 70% is 206.5, which is 8.13, so an 8 incher would be used.
So then, a 295 on an 8 is supposed to be 295 +/- 5mm. But on a 10inch wide rim, which IMO is still too narrow, that is 2 inches wider; this 295 is gonna be less than 50mm/more than 25mm , wider. At a measured 330, this is 35mm wider so 1.4inches. So you gotta figure this into your equation when ordering your custom-backspace wheels.
Furthermore; generally .5 is the recommended minimum sidewall clearance.
At my lowered rideheight with nearly flat springs that each of which has an extra full-length main leaf, and mounted on Poly bushings, body side-shift is minimal. I can get away with just .25 inch. So you gotta figure that in as well.
I can't give you a backspace cuz my rear end has been narrowed to fit a standard 4.5" backspace wheel. Please note, at the tread, and about 2 inches down over the sidewalls, these 295s are still inside the wells, both sides. This the only legal way in Manitoba, to run them without flares. If a cop pulls me over, it won't be for tires sticking out too far.