Old Tire Size Conversion?

That actually looks a bit tight up front. The places I had big tires clip the edge of the fender was the top but watch th efront and rear corners of the opening as well. Probably when compressing (going over bumps) and the steering turned left or right. Not sure how similar Barracuda front fenders are to the Dusters. In any any event, the risk will go away with the 215/70 tires.

440s were an option for the Barracuda in '69. There's a reprint of the Car Life road test in the Brookland Books Plymouth Barracuda 1966-1974
It says the torsion bars were 110 lbs / in - which could be the .89" dia bars. I vaguely recall seeing a listing for slightly larger factory t-bars but don't recall where. I could be wrong. In any event, once you get the new tires all around, just crank the t-bars up or down to get the factory settings.

Same article lists rear leafs as 150 lb/in - which might be a unique spring pack for those cars - maybe based on the 383 leafs which had a different main leaf than the others according the parts books.
Tires were E70-14 Goodyear "wide ovals" on 14 x 5.5 rims

You may have to change speedometer pinion to get the odo and speedo calibrated for the tires you end up with. Pretty easy.