I bought the partial quarters for my Dart years ago but once AMD came out with their full quarters, I went and bought a set and tossed the partials in the attic.
This is one of those jobs that if you are going to take the time to do, then do it right and use the best parts available. The partial quarters take a lot of body work to make them look good and when it is all done, you have a quarter that has no rust but has a ton of body work done to it.
The quality of the car you end up with reflects the quality of the parts you use. Your car may look great when you finish but the value of your car will also reflect what parts you use and for the price difference, the AMD quarters are worth twice what they sell for.
From the looks of the rust in your trunk extensions, you are going to need them as well and it will be a lot easier to get everything you need from a good manufacturer so it all fits correctly.