how to tell if 70 Dart is real 340

If you have the VIN plate for the dash and it matches the door sticker, fender tag, and the radiator core support stamping, I'd have to figure the car is genuine. All the other parts mentioned can be transfered from another car. The RH rear exhaust hanger bracket is a 340 only part and is welded to the floor so that's another one hard to fudge but not impossible.