I think the 1/2” relocation is worth it, on a Duster/Demon/Dart Sport it will let you run 295’s and actually have them tucked into the quarters. Without the 1/2” relocation you’re only going to be able to do that with 275’s. Not gonna count the guys with SS springs and 4x4 ride height that have the tires outside of the quarters.
The “3/4” location is not a 3/4” relocation. It is physically impossible to move the hangers inboard 3/4” on these cars. I literally use the MP hangers on my Duster, they’re a 1/2” offset. The shackles are a 3/4” offset, but all that does is put a bind on the springs. If you move the perches 3/4” it will bind in the front half of the spring, if you move them a 1/2” it puts the rear half of the spring in a bind.
I use the MP offset hangers with the spring perches moved a 1/2” with rear leaf spring sliders that I located a 1/2” inboard from the OE shackle location, the MP kit only screws things up if you use both the hangers and shackles together. Although the DoctorDiff kit is nicer, the hangers are better quality and don’t require dimpling and drilling a hole in the frame rail like the MP kit does. I’d wait on the DoctorDiff parts myself.
The B rear is useful but it depends on what you want to do for wheels. In the 18x10” size there are a lot of wheels in the +12 to +20 which actually work well with the A-body width 8 3/4. I run a 68-70 B rear in my Duster with 18x10’s, +38