I'd say there's more than one out there. 1970 Gran-Coupe, 383 4bbl, pistol grip 4 spd in FM3.
If you start to break it right down into options many cars would quickly become 1 of 20's etc etc.....
When I spot a 1 of # car it's usually classed on year, paint (+ stripes), interior colour and engine.
Unfortunately, there isn't any real way of knowing how many of what cars were built.
The only true way would be to gather all these cars on the worlds biggest field and break them into categories, including the Mopars in heaven, so, as you can see there isn't any way to know how many were built.
That's not to say you still can't go out and find others like yours at shows and on the web.
Nice car by the way. I'm not a fan of Panther Pink but I sure as hell can appreciate them.
Even if it's 1 of 20 it's still rare....at the end of the day, does it really matter!?