Why don't you just call Cass!!!
did it make a difference in tire clearance? I looked under there years ago and decided it was minimal gains.I put them on my 64. I think the difference is the spring bushing bolt hole. I used springs with the larger front bolt hole so they worked well. If you are keeping the original size front spring bushing hole the special supplied bolt will be too large. If you have the larger bushing all will be good.
FWIW....MP 3/4 inch off set shackles, front hangers, moved spring pads, 275/60x15 M/T Drag radials, 15x8 rims with 4 1/2 inch BS, rolled the lip of the wheel opening
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.You may want to use "search" here for options. I don't know for sure if the Darts and Barracuda's are similar but My 66 Dart has 15x7 4" b/s wheels with 225-70/15's and no clearance issues. I bet with a specific offset and a little lip trimming I could fit a 8" wheel in there. But like I said, Barracuda's may be different. New 15" rear tiresView attachment 1715207540
I gained the claimed 1/2" spring clearance for each side on my 64 Barracuda. I narrowed a C-body axle housing to be 1" narrower than the factory A-body housing and that centers the wheel in the wheel opening. I have 245/60R15 tires on 8" zero offset wheels. The result is 1" clearance to the outside of the springs and approximately 3/4" to the inside of the inner wheelhouse. My car is slightly raised so it leaves plenty of room. Might get pretty snug on a lowered car.did it make a difference in tire clearance? I looked under there years ago and decided it was minimal gains.