Narrow rear end.

To give you an idea. I had a 68 dart, what I did is I bought the wheel & tire size that I wanted to run ( 15x10 w/ 5in back spacing ) & a 325x 50 x 15 tire. I put them up in the wheel where I wanted them to be, then I measured the space between the back of the wheels. I ended up moving the inner wheel well in to the frame ( 3in ). Put in a spring relocation kit. Narrowing the rear 3in from each side. I like a lot of wheel dish on the outside. It gave me real good clearance all around. O & used a stock A body rear to narrow . The barracuda is a little diff. You will have to deal with the back of the back seat. Plus if yours is a fold down seat & want to keep it a fold down. My 69 came with a fold down seat & I wanted to keep it that way. So I only moved the wheel well in 1 1/2 inches. I also narrowed the rear 1 1/2 in. from each side, & I also put in the spring relocation kit. I get a 15x 8.5 rim with a 275x 60 x15 tire on it. Good luck Let us know how you make out.