Have a new rear door plastic trim piece all painted and ready to install the  chrome hinge to it. I purchased the rivets and chrome and now need to rivet the hinge for the doors to the plastic trim piece.  I cannot find a rivet gun that will accept the rivets that came with the trim/hinge. I have checked auto and tool stores and cannot find  what I am to use to squash the rivet that holes the chrome hinge to the plastic trim like the original trim piece.  all the store rivet guns uses longer stems and then the rivet on the end but they will not acept the rivet that I have.  The head is about 1/4  inch wide and the stem is about the same and 1/8 diameter. but how or what do you use to compact it to hole the two items together without breaking the plastic trim????? do yo have to go to a machine shop??? help?

Hmmmm.....I'm not sure on the '78, but on the earlier cars, originally, the plastic trim was secured to the doors with plastic rivets.
The replacement plastic trim is held to the doors with screws, and the hinge is held to the door with screws from the factory.
Are you saying that your hinges are fastened to the door thru the plastic trim, and not directly to the doors themselves??

I know my  original mesage was not clear but the Plastic trim that surrounds the 3 door panels has a chrome hinge mounted to the plastic with rivets. the the doors themselves attach to the chrome hinges.  The original had the Plastic frame and chrome hinges attached with rivets. But not the rivets that yo see at sears or HD, these were just 1/4 inch ling but still had to be squeezed flush. I could not find anyone who knew or had a tool to do this.  end result found what look like rivets at Home Depot that were about the same size and you can screw in one end to tighten them and they look close to the original.  I tried body shops called manufacturers onlne who sold these rivets but no one could tell me the tool to crimp them with. just that big manufacturing companys had the tool but not something I would buy for 6 rivets. Thanks again for you interest, but still curious how they were originally set. with something us common folk do not have in our tool boxes??? Thanks now onto the next project.

Those are factory rivets.  There is a special rivet gun available, but not through standard tool suppliers.  You need some who supplies body supply tools.  You can get it from Matco, Snap-On, etc.  But it probably won't be on their trucks.