Father-Son 1974 Duster Project

Yes. They are the MP relocation kit that you weld the "pocket" into the frame. The inner wheel tub is the inboard limiting factor.
However, the Doctor Diff kit will work the same. With Doctor Diffs hanger and shackle the inner wheel housing becomes the limiting factor for inboard tire clearance as well. The only reason to ever NEED a MP-style (in the frame) relocation is if you mini-tub. No reason to go that far if you want to leave your factory wheel tubs alone.

I'll try to find pics but the car already moved ahead of me. I am getting the hell outta Cali!! Car's at my Dad's in Oklahoma.
I already have the mopar offset spring relocation kit in my dart sport. 8 1/4 rear as well. 5.5 backspace seemed to me like it would come very close to springs. That is why I asked. By the way that is the perfect tire wheel combo ever!