New Exhaust for my Duster?
I would go over the rest of the car really careful since the exhaust is cobbled together like that- who knows what else is done with the same quality- electrical, brakes, brake& fuel lines etc.
For exhaust I would leave the 340 manifolds on it, get a set of 2.5" headpipes from TTI and get the 2.5" dual exhaust kit from summit or jegs- it comes with no name but decent quailty turbo mufflers or you can order just the pipes/hangers/clamps and add the mufflers of your choice.
If this is your first Mopar you don't want any part of installing headers on an A body yet, I can get a set on in about 2 hrs but If you have never done them before it will be a weekend full of cussing and bleeding.