So this is a bit of a trip for you but might be worth considering...in Southern California, there is a huge Mopar show every April (Soring Fling) and every October (Fall Fling). They have a huge swap meet at both events. You can probably find a lot of the items you need at bargain prices. I always see big sheet metal items for our cars. Every show, I come home with tons of cool finds. It's like Christmas. People are really cool there too.
Another advantage is the car show itself. You could examine dozens of Challengers and take reference photos of the things you need to aid you in your build. Seeing how things fit together up close can sometimes be way more helpful than a few photos. You might even find one that was converted to a 70, then you get the benefit of talking with the owner to learn more about the small details.