1966 Dodge Dart GT - Trying to Determine How Rare

Remember, production numbers are just that- how many were produced. "Rarity" kind of refers to how many may still exist, and that's going to be quite a bit fewer; and a lot harder of a number to nail down. And rarity doesn't always equate to higher value, as noted by others above.
In my opinion, any car that has survived 57 years and is still in the kind of condition yours appears to be in deserves a little lovin'.