I know this may not be what you are looking for but Ma Mopar made the best fitting sheetmetal. If you can find good original OEM stuff, it's the best route. If you need quite a bit of it, perhaps a parts car might be wise. As mentioned above, if you are limited to aftermarket sheetmetal, AMD is very good.
I could not agree more with GTXperience, if you can find oem, that is definitely the way to go. AMD is likely the best aftermarket, but nothing fits like oem or nos. I have been restoring a `68 Road runner and have replaced most of what is shown in the picture, including rear frame rails, trunk floor, trunk floor extensions, wheelhouses inner and outer, package tray and the surrounding understructure of the roof, trunk hinge brackets, rear tailpanel crossmember, shockmount crossmember, and the whole cowl section including the firewall, upper and lower cowl and the forward doorjambs, also not pictured is the radiator core support. The only 2 pieces that I replaced with aftermarket parts up to this point are the trunk floor extensions. I will be using oem door shells, fenders and hood, but I did pop for a lot of AMD metal for the backhalf of the exterior sheetmetal and have had it screwed together recently to check fitment and to make sure that all of the structural stuff I have doon was right. I will say the AMD metal fits decent, but not quiye like ma Mopars original stuff. The other thing is that by using oem stuff, and it is out there, I saved thousands of dollars and likely saved a car that may or may not have been worth restoring in a lot of peoples eyes. Oh yah, the interior floorpans will also be AMD.