Traction Control Needed...

If you smooth off the high spots on the inner fenders, you can run pretty tight,say1/4 inch, The tires will rub on aggressive turns, and it's like applying the brakes on a bicycle, but the sidewalls can take a bit of abuse.Slow down
This smoothing takes a big hammer,an iron rod,a good aim and a courageous helper. Eventually you will hit the shock support, and that's that! So just go there first, the tubs only stretch so far.
Since the sidewalls are now the body sway stoppers, you can run pretty tight to the fenders too. However, on the outside, as the wheel moves up into the tub, it encounters a huge rounded part in there and rubs on that. So then you have to increase the rear ride height. This makes the springs easier to twist, and so the tires rub sooner and harder on the tubs, limiting cornering. Eventually you get tired of that, and increase the inner clearance to 3/8, decreasing the outer clearance, and inviting a sidewall cut there.
But if you promise to corner really slowly, and avoid speedbumps, and potholes, you can run even closer than 1/4 inch. Just don't be in front of me more than once,lol.

The truth is, to deal with a stout SBM, and on the street;
you can't install a wide enough,or tall enough,street tire in even a Big-Tub A-body,(Duster/Demon/Barracuda) never mind a Dart, Scamp, or other.
So you have to find traction in other ways. You're gonna have to employ weight transfer techniques. Open your wallet and dig deep.

The ET difference, from zero to 30 or even to the top of first gear, without traction aid,being on the tallest, widest,fattest tires that will fit in your tubs, versus what you have on there now, is IMO, not hardly worth the time and dollars to get them in there. Having gone down that road, that's my opinion.
But those fat 325/50-15s surely do look good in there.