the chassis tag should match the chassis no which is stamped in the d/s floor pan, I personally think it is a copy, no sunroof door locks are chrome, 3dr they were black plastic type, the aerial looks like a pull up type, lookas as if there is a chrome strip in the rear window, all of which were on the lower models, 3dr were not registered in 84 either, It need a lot more investigation i think before parting with your cash.
Good luck
Paul