Not to be mean here, but it doesn't sound like you have a lot of experience on these cars or specifically with a 6 pack (6 barrel for a Plymouth). These are not usually "bolt on and go" deals unless you buy everything brand new, have all of the other vehicles operating systems working correctly (electrical, cooling, etc) and can properly setup and tune the 6 barrel. They are not magic or anything, but they generally take some work to get running correctly and keep running. Understand that buying used stuff (especially the carbs) is probably going to lead to a lot of frustration and cost. That said, if you had someone local that had a good running and set up system on a car and you could purchase it and do a direct swap, it would probably work out. Many if not most of the used stuff you will find has been abused, sat for many years (sometimes with fuel in them) and/or been modified somewhere along the way all of which is going to lead to problems getting it to work.
Not much is as cool to look at as a 6 pack/barrel system but they can be very painful. I just removed a big block 6 pack system off my Challenger and installed an EFI 6 pack. The carbs never did work all that well especially on a hobby car that gets driven every once in a while. I have run big block and small block systems over the years and each one has its own personality commensurate with the car it is in.
Lastly, understand that a 6 barrel system flows more fuel than your 318 is going to need or like meaning that it isn't going to be a rocket just because of the intake system. Yes it will bolt right one and look the part, but you need good heads, a decent cam, good exhaust, and solid ignition system to get the performance out of it. Don't let people tell you that it "only runs on the center 2BBL until you step on it", the reality is that the center carb does "most" of the work but the end carbs flow fuel even when they are not opened up by the vacuum pods.
look at a FITECH EFI system (basically a 4BBL); cheap, easy and you will love to drive your car as a result. If you want to 6 pack look, get a 4BBL oval air cleaner system (came on 4BBL roadrunners and is available new, the base is unique to the 4BBL but the air cleaner element and lid are interchangeable).
Hope this is helpful
Oh BTW; while the AAR is definitely cool, the Gran Coupe is just as cool (probably even more so since many people clone AARs). Your car, do what you want but the Gran Coupe status is worth preserving.
