I believe I stumbled upon a '68 or '69 Belvedere...

Well, it still may be a savable car even though it doesn't have the correct fender tag. That is depending on whether it or the tag were ever written off. Does the tag match the dash VIN? I am having a hard time believing you took the tag off the car. Aside from it supposedly being incorrect, that is a vital part of a Mopar. Was the color under the tag repainted? Is it a 4spd car? Clutch pedals? In any case, we'll be waiting for pics.