sorry, I can't help on the gill fender patch panels, but unless your fenders are other wise perfect I would suggest replacing entire fenders with new 71 fenders.
I did have a friend who worked at a body shop and had to weld in those patches on a 70 model, for a resto-mod, uncertain of the brand, he's very talented, but said they totally sucked to blend in properly. if you do go patch avenue I am sure someone with originals here on CC can snap a few pics and measurements to locate them correctly...
Now on the gull wing front, I spent a few years shopping around purchasing and returning a few gull wings before getting one from josh's muscle car parts, and it was pristine. hundred less then else where and perfect...however it does not have the ever so ridiculously pricy pentastar molded into the wing.
this really seems to be the deciding factor for price, so pay attention whether it has that or not. if you care.
also pay attention to if the wing is "ABS" or "composite" (vague term for fiberglass) as originals were ABS,
the legs/feet should be hollow aluminum, not solid. Again this all depends how much you care if its close to original.
If I remember correctly the cheapest I found with the pentastar was around 600, crazy. wanna say josh's was around 300.