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

I personally believe that custom cars are built to the owners liking. So in a sense, they are worth less. I also don't like the shaved handles and believe that rare cars should be built relatively stock. BUT........

I also believe that you should make the car your own. Do something that makes it stand out from the crowd. Nothing worse than going to a car show and seeing 20 red cudas. Can't tell one from the other. My numbers matching 340 4spd Duster is going to have some of my touches that many people probably won't like, but guess what. It's my car and not theirs. Do with it what you want.

Another thing. If it is missing it's fender tag and build sheet, yes. It's still an H code, but that's all you can prove. The value has already gone down as far as a perfect resto project.

Have fun with the car, build it safe and how YOU want it. Don't worry about what others think, they don't own it. Welcome to the site.