'71 Dart & min-tubs how much tire will fit?

does this look like it will work?

You can get about 15" of tire width from the frame rail to the fender, if you roll the lip and push the quarter out a little but the real issue is the wheel opening. Without stretching that no way you will get that to fit.

Sure, all it takes is money !

Definitely will have to stretch the wheel opening length.
Not sure if that rear axle is too wide, looks that way.
More info would be handy, unless you're just kidding.
13x31s ride under my Duster using its original rear rails.
Worst case, new rails further inboard, tubs and some under-car cussing...

With mini-tubs and 10" rims, 325/50-15 tires will just fit if you have the right backspacing (7.25" for a stock A-body width 8-3/4).
I have 295/50 on mine and there's loads of room. Well, "loads" relative to most things on an A-body project

it's 325/50/15s on 15x10s with 3-1/2" backspacing - yes, it fits

when I mocked it up on the jack stands, I thought NO WAY!! what did I miss

Are those the "Shelby 500" slot mags ?

they are U.S. Mags (reproduction U.S. Indy Aluminum Slot Mags) from Summit

15x5 front w/2.5" backspace 15x5 US INDY
15x10 rear w/3.5" backspace 15x10 US INDY

I think the rear axle housing ended up 50-3/4" flange-to-flange

Those 325/50 15's are a bit shorter ( - 0.19") but 2 inches wider than the 275/60 15's I have under my stock wheelwell 1965 Barracuda.

this Dart had 275/60/15s on 15x7.0" Rallye wheels before the & commenced

How much did you end up "stretching" the rear wheel wells?

a chassis shop moved the inner rear wheel well in flush with the frame rail, where the Caltracs were/are mounted - the outer wheel well is "radiused" to remove the "hump" just above the wheel lip

AFAIK the rear wheel lip is the stock profile with stock wheel lip mouldings, the lips are hammered & trimmed - I will confirm how wide the added material is in the wheel well