Buy an NOS RH quarter for $900-1K. The RH quarter stampings suck. D.corn and G. Legion. Unless you get AMD quality substantiation.
Last autumn, non AMD: Contour incorrect at rear bumper/tailpanel, needed extensive mods. GM door upper bumper did not contact quarter jamb, required .375" mod. Quarter window top inconsistent and much higher than door. Trunk weatherstrip area stamping awful; I grafted in the old quarter's gutter area. Rear window channel too shallow. Astro door vent in wrong location, Door jamb reinforcement recesses poorly stamped, lack definitiion and shallow. Wheelwell contour incorrect (where the molding sits in the radius). Wheelwell flange too narrow, needed material added. Lower door jamb too short, needed extension. The stock was placed in the press wrong thus justifiying the material to one side, which resulted in shortness.
LH G.L. quarter fit fine with only slight trunk weatherstrip area mod. Typical edge definition lacking, no big deal.
I've been doing this for over 20 years, don't mind metal mods and expect them, but the RH was ridiculous. Aftermarket quarters are not heavy guage unless AMD. A friend has ordered an AMD RH quarter because his others sucked too. I am awaiting product evaluation. Because AMD is heavier guage, you are better off anyway, even if the fitment is not perfect. Never expect a panel to be perfect either.
NOS sheetmetal does not always fit well but will not be nearly as bad as a RH repro (unless AMD possibly). I've hung NOS quarters that fell on the car, but they were good stampings. The NOS RH fender the customer gave me needed the lower portion modified for correct rocker mating.
I'd suggest telling the vendor he will eat the return shipping if the panel is garbage. And don't believe him if he says it's good. I returned quarters to Ground Up no questions asked and a different vendor insisted his were better. Only the LH on was, his RH was garbage. The labor to repair the repro quarter exceeds the cost of NOS. Matt's Classic Bowties was running a special on AMD quarters,$389 shipped. Another vendor wanted $515 shipped. So shop around.