I have a pair of the fiber glass extensions on my 9/19/68 Metuchen Mach 1. These don't get talked about much. So the when, where, and why they were installed is not clear to me. What I have learned is that they were installed on the very early production cars. It seems all three plants used them until the stock was depleted and then the metal version was introduced. It may be that all the Shelby cars received the early glass version ? This part number photo, from my car, has the FORD logo. This part has a C9ZB part number and a GB part number. The GB part number can also be found on the fiber glass interior parts of my car. Additional information or experience's ? Brian