"Is it possible to build a numbers matching car, if all you had was the paperwork and fender tag from it?"

It is possible to screw the fender tag to your car. It is also possible to get a VIN plate made to rivot to your dash. But the whole context of numbers matching would be engine and trans as well. It is also possible to track down the engine and trans to the new VIN. It is even possible that some one kept the body number to graff onto another core support/body. So in theory it is possible to build a numbers matching car from the info provided on the fender tag. It is called a rebody and it really shouldn't happen, but I'm no the police, just opinionated. A rebody is worse thatn a clone in that with a rebody someone might get duped one day.