tail panel swap in progress

Are you putting a new '76 tail panel on?

I ran into a similar situation when I used a later model ('74) trunk pan on my '72 Duster. The '74 trunk pan had an indent along the rear edge, where the Duster's tail panel was flat. I welded the trunk pan where it did meet, and used 2-3 thicknesses of scrap sheet metal to fill in the gap where the trunk pan had the indent. After it was welded up and seam sealer applied you couldn't tell the difference.
C