[Ben M.]

It's unusual solely because it's in great shape and 52+ years old. That alone makes it "rare" nowadays. As far as modifications, adding disc brakes and a posi rear or doing some minor motor mods will NEVER result in lowering the value of the car if you use factory style components and keep the factory stance. If you go full airbags, 4" drop, big wheels, or turbo LSx, you'll lose some value, gain some other regarding trying to sell it.

At this point I would drive it and do the disc brakes and better rear end at a minimum just because those things don't hurt value and make the car safer and more fun to drive. Anyone who complains about those mods when you go to sell the car wasn't interested in buying it anyways.