Your truck is not a factory piece. It was modified by the aftermarket. Your Grandfather possibly paid a body shop to modify a standard long bed Integral cab.

Looks like a good job. Post some pictures of the profile and of the inside steps of the rear doors, hinged and B post. From those i can tell if they are Crown Pieces.

Also post as suggested a photo of the data plate located on the drivers door.

Where are you located in Arizona?

Garbz.