is my car in any way special/rare or more valuable than any other? 70 340.

The muscle car market is weak right now in keeping with the rest of the economy but if the car was all put back together as it came from the factory, I would not see you getting much more than your 15K that you already have in it. Most guys that are going to extensively customize their cars start with a good, clean, straight body, but one that has a less desireable drivetrain from the factory. That way there are no tears shed altering a car that is rare and has much more intrinsic value, like a factory 340/383 car. Like 68383gts posted, there were less than a 1000 made of that exact model/configuration but it`s your car, you bought it and you should do what you want to do with it.