So I'm gonna disagree with one thing, the lower fender to bumper brace absolutely came on cars with front valences. All of the '70-'72 Darts I've seen have them. Both of my '71 GT's have them, both of the '71 front clip donors I got parts to convert my Duster over to a Demon had them, and so did a few of the extra '70-72 Dart fenders I've picked up. So not having a lower fender to bumper brace is a Barracuda thing, not a front valence car thing.
I'm also gonna re-emphasize that these cars have really large body tolerances straight from the factory. The rubbing on one side doesn't have to be because of an accident at all. The small amount of interference, compared to the small clearance on the other side, could 100% be the result of the factory tolerances. No accident needed. There are dozens and dozens of threads on this forum about a tire rubbing on one side and not the other. The suspension points can be off by as much as a 1/4", that's before we even start talking about the body tolerances. So honestly, I wouldn't be that worried about the frame rails unless there's a buckle or wrinkle in the rail somewhere.
Your 6" rims with 3.5" of backspace aren't helping either. That's a 0 offset rim, but you have the BBP brake conversion. All the BBP cars had +6 offset rims, so, for a 6" rim that's 4" of backspace. That 1/2" of backspace would likely solve all your issues. The other thing is, a 235/60/14 isn't going to solve your issue. Yes, it's shorter. But it's going to stick out almost another 1/2", which is too much. The lower front corner interference is on turning, not straight ahead. So, the tire height is part of it, but so is the width. Shorter is helpful, wider is not. I would bet the 235/60/14 would hit just as bad because of the added width. Especially with that little backspace.
The suspension modifications can help, but they're not a slam dunk. Using the UCA's to add positive caster might move the wheel back slightly. But, it will also cause the wheel to camber more on turning, which might not help. The strut rods are another matter. If you make them longer they can help, but that will reduce your positive caster and that's not good for handling. If you use the strut rods to add positive caster you're actually making the strut rod shorter, which will make the issue worse. Remember that caster is just an angle, tipping the top of the spindle back adds caster, but so does pulling the bottom of the spindle forward.
And then there's the issue of suspension binding. The strut rods are not there to adjust caster, they're there to locate the LCA. If you use them to move the LCA too far in either direction they will cause binding in the suspension, and you don't want that. I don't think any of the alignment adjustments are going to get you a 1/2" of clearance anyway. There may be some clearance to be gained that way, but not that much.
By far the best solution to all of this is to get a set of wheels that have the right backspace. With a 14x6" that means at least 4" of backspace.
