Trim and Emblem replacement questions?

On the ones I have for my 79 Monte Carlo the lower rivet is actually a locating pin as seen in the photo's below. Your back plate shown is missing the top hole and the top portion behind the knights top plume.

The lock cover on the right is a NOS part I found at a dealership selloff. The part on the left is from another 79 I had. Pictured above is an interior trim screw and "U" speed fastener that I used to attach the lock cover through the top hole. No rivet needed.
Using tape and a long screw driver I was able to attach the speed fastener inside the trunk face to the trim screw. Made removing the cover for detailing easy.
Sorry to be late with this information but maybe it will help.

On mine the bottom pin located it in the trunk lid and kept it from rotating once the screw on top was snugged up. I never used any tape on the bottom due to the base having a "drain port" for lack of a better description and not wanting to block it. The bottom pin actually was a snug fit to the opening in the trunk lid.

Zeus1978 said:

Ok i can disassemble and punch a rivet into the bottom hole and work it down , or open the hole in the trunk until i get a snug fit. Thank you for the info

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Before you disassemble the cover see if the pin on your cover does snap in to the lower hole of the trunk lid. You should not have to punch out what is there, just push it into the lid then attach with either the rivet at the top or use the trim screw method.
There should be a slight shoulder on the pin and top attachment point to provide a positive location in the trunk lid.