The first 300 plus 1965 GT350 Mustangs had their batteries relocated by Shelby American to the trunk for better weight distribution. When the stock front battery tray was removed, four of the mounting holes remained in the front apron. Shelby American sourced unique rubber plugs in order to fill these holes. Apparently, these plugs were not a stock Ford part. They were perhaps just some type of aftermarket plug. I'll also note that some cars only received three plugs, since the original bottom front battery mounting bolt sometimes still remained in the hole!
The rubber plugs were really designed to fit into a thinner panel. The original plugs actually get "sucked down" in the hole and distorted as shown in the above image.
These plugs are just about impossible to find, and even if you are lucky enough to have the originals, they are often weathered, hard, and cracked.
I always thought that it would be really nice to have these plugs available as a reproduction. The problem with reproducing a part like this is the simple fact that not many of them will be sold relative to the high tooling cost to make them. I decided to do the project anyway, hoping we could just break even on the deal!
Anyway, the plugs turned out fantastic! They look and fit just like the originals. They are great pieces to have available for owners of the trunk mounted '65 GT350's.