Numbers matching ?

Can someone tell me
Hemi Barracuda 68
We're their engines matched to the cars like all mopars ? IE V code 6bbl engine to car can be distinguished if its original or not. What about the 68 Barracuda originally Hemi car.
Reason I ask seems there is one for sale.. and the gent that's not possible but he claims he is the original owner.. Yup.
Thanks
MAPS