Plymouth duster rear suspension questions

Hi everybody I am getting started on my rear suspension and was curious about some parts that I need to order. Purpose of a vehicle is mixed between daily driving and canyon driving. The front suspension is almost done and now moving on to the rear I have the following parts.
- Ford 8.8 with discs and limited slip
- rear bilstein's shocks
-US car tool spring relocation kit.

After browsing with some of the forum post here something that I think would match my front suspension PST 1.03 torsion bars and sway bar. Would be a set of Mopar performance leaf springs.

I'm trying to figure out which ones I should use
Between the following part numbers
P4529415 and P4529414.

I understand that the difference is 1-in arch but I don't understand what that means in the sense of suspension geometry and a effect.

Additionally I've read that these leaf springs take a 1-in bushing and so I'm trying to additionally find a set of rear shackles that will also work with the relocation kit and the new rear leaf spring setup. The ones that Mancini racing seem to be a fairly good price point and have polyurethane bushings but I don't understand if they'll fit my application as there's many aftermarket variables.

If part numbers could be included on the shackles/bushing kits that would be very helpful thank you

The difference in arch is 5.5” vs 6.5”, so, the 1” you already know about. The 5.5” arch is a “zero arch” spring. The spring will be nearly flat when installed. The ride height will pretty much be factory, maybe a little lower. Think about the same height as worn out original springs, but higher than hotchkis lowering springs.

That said the quality of the MP springs has been all over the place lately, so, what you get may be different. Honestly I’d look at the Hotchkis springs.

With a 1/2” offset and a quarter lip trim you can fit 295’s on a Duster. I did. 295/35/18’s on 18x10’s.

Bryan, I would advise you to use @DoctorDiff 's 1/2" spring relocation.
It is pointless to do the "in the frame rail" relocation if you don't have the car mini-tubbed. Furthermore, if you are going that route it is good for fitting a slick or big tire to go drag racing. For handling, it moves the spring too far inwar for handling dynamics and will straighten out your leaf springs. Mopar built these cars so that the leafs "toe in" at the front hanger. This does a lot for handling.
Moving the spring perch and leafs in by 1/2" will put it under the inside of the factory wheel tub and keep the "toe in". If you aren't mini-tubbed why would you need the leafs any further inboard than the wheel tub?

A-body springs don’t toe in, they’re straight. Parallel to the frame rails. E-body springs are toed in.

The angle on the springs is arguable anyway. It helps turn in by inducing some rear steer, which can be an advantage. But it also makes the car looser on the exit. So it depends on how the car is set up.

Regardless A-bodies don’t have it. The inner fender is limiting factor after the springs, so I totally agree there’s no point in doing a 3” relocation without a mini tub. The 3” relocation does change your shock angles, which isn’t great. It also means you need stiffer springs to control the rear axle (longer lever arm acting on the springs from the contact patch to the spring).