mine is a bfg but I bought it used off ebay. There were many other space saver tires sold in GMs and Fords back then. Those cars were sold in much more volume than Mopars so those will be the common ones you will find, so if originality is important to you you have to shop very carefully. I would guess that most people selling these either are ignorant or being deceptive about what they are selling.
Like I said, I have the BFG F78-14 tire, but I think it is from a 70 Mustang, so the coding on the tire is probably different, and though the bolt pattern of the rim is the same, the rim itself is slightly different. Unless you are an expert you cant tell the difference, but my car is a clone, and Im not being deceptive about what I have. Besides, you would be CRAZY to actually use one of these for its intended purpose. At this point they are for looks only.
As for the value, I dont know. Sorry.