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

I just read throught the whole thing too. It's your car so you can do as you please. I have a question though.

How do you know the car was originally a 3 speed?

The reason I ask is that, if you're making an assumption that it's been converted based on the sloppy way the floorpan is cut where the floor hump is, all 4 speed Mopars came like that from the factory, no extra charge! :-D