There are several places that the factory VIN was located. If the car hasn't been repainted, look under the doors, inside fenders area (where hood seals), under hood, nose cap, under trunk lid. Look for a sticker with the original VIN in any of these places. If it has been repainted, hopefully they just repainted over these decals. Just carefully clean off the paint to reveal the original VIN.
I don't know if there were any hidden stampings somewhere on the frame, etc... but I'd look for the body tags first. If I had a Mustang I'd send you photos, but I don't.
They're white stickers about 2 inches long by .5 inch wide.
Good luck,
Steve
1999 Ranger 4x4