The R&R (Parsons) resin was advertised as a '64, but it is a generic 60's panel ... there were no meaningful differences in the bodies from 1960 through 1966 ... [The only visual differences year to year were hood configuration, grilles, and trim details.]
The R&R casting does not come with grille or hood ~ you need those from your donor kit ~ so it works for any year '60 through '66.
The biggest issue with the R&R casting is that the rear roof overhang (above the rear doors) is greatly exaggerated and inaccurate. It will take a lot of work to make it conform to the actual vehicle's contours and appear anything like the real thing. I have had an R&R casting for years and have never attempted to build it, primarily for this reason and secondarily because mine was so badly warped when I received it - just more work to correct the roof than I cared to tackle on a warped body.
I'm guessing the R&R casting is a copy of the AAM (All American Models) casting, but I don't know that for certain. AAM has been out of production for years and years, and I've never had one to compare. But, it has been common for R&R to copy other resin casters.
Hope this helps.