look again, if it was rebodied, somebody went to the trouble of removing the radiator support. Look at the welds, most people are crappy welders, does it look original? there are two sets of numbers under the drip rail, drivers side, people sometimes mix them up, they can be close together. one is the car, another is a parts stamp that means nothing. my GTX has that as well as the vin, about six inches away.
If the car has a sway bar, 10 inch brakes, 8 3/4, and a second hangar for dual exhaust, then somebody went to a lot of trouble to clone something, or it is a GTS. Look to see if the bracket for the right exhaust was tacked on, or properly bolted on.
it takes some thorough examination to really be sure. Is the windshield and seal really old,(assuming it is in the car) The trunk lip number is the only other number that year. Does it look like someone replaced the whole Quarter? Look at the color ID on the build sheet. do you see that color anywhere inside, or left over and missed by bodywork? it can be difficult to be sure, but an experienced eye is what you need here. Match all the options you see on the car, and see if those codes are on the sheet.Buckets, floor shift, manual or power, A/C, etc. Vinyl top or no, the roof attachment to the Quarter will tell you. it is highly unlikely a thief would be able to secure a car identical in every way to switch. That build sheet has far more Info on it than a fender tag. Sorry for the long post! I hope that helps.