can I do this and how

If you run 73+ spindles with an early sway bar, the lower control arm sway bar tabs keep the spindle from turning very sharply. The spindle will hit the tabs. I have done it, and needed to grind the tabs in order to increase the turning radius.

If you can easily get your hand on a later K-member and sway bar setup, it might be an easier way to go. I had 17" wheels, so I don't know about wheel contact. I doubt it, though with 15" wheels and only 3.25 offset.

I would be concerned with running an 8.5" wheel on the front with only 3.25" backspacing. That wheel is gonna want to stick out from under the fender.

This is a picture of my 67 Dart that had 7" wide wheels, with 3.75" backspacing, and the same brakes you're talking about.. The wheels you describe would stick out 2" farther than this. I know a Dart and a Barracuda don't have the same fender, but it would be similar.