63 Dodge Dart, now let me see;)

Dne007 said

measuring from the mating surface to the most outer lip of the rim is 3 3/4
Just got a call from the Tire store~ he's ordering a wheel from American racing with 4.5" back spacing~ , plus 8" width vs my 7"

56 1/2 for the rear axle, flange to flange (flange meaning where the drum mates to.

Click to expand...

Good Lord,.....only increasing the backspacing .75" & increasing the rim width 1.00" means the outer sidewall will be another 1/4" into the outer side of the tub,....NO that will not fix it, whether those 255's are a bit too wide for 7" rims or not, 8" rims won't fix anything & completely negate the gain in backspacing......
Massaging the tub is risky because there is a very small gap on those bodies tub-to-quarter, by the time You get the area to stretch into enough permanent deformation, it may come into contact with the quarter skin & screw up paint/filler/etc., heating & a hammer would've been the move before the car was finished......
Getting a 7" with the correct offset or downsizing the tires are the only correct fixes here. Not sure if the N95 'stangs ever used 15" rims, but they had more of a higher backspace style rim, but probably be 16"-17" only in the option wheels available.