My mustang is a Dearborn, August 12th (late) 289 hipo, GT. I have owned the car since 1981. I disassembled the car back in the 80's and stored the parts waiting till the time of restoration. Well I am deep into the restoration and learning all kinds of things about the car. This Forum has been a great help. I had 3 fire wall pads that I had all packed away in a wooden box I had built for them. One of these 3 pads was out of the Hipo fastback. Back in the day I was not aware of the different styles. I have learned this info from this forum. At first I assumed the firewall insulation pad for the hipo was one of the black non-dimpled styles I had. But after studying the holes in the pad and the info about these pads on this forum I am now convinced that the SJ dimpled version I have is the one that was originally in the car. Specifically the hole for the Hipo choke cable shows the evidence of a cable used in the hole. The other two pads have never had a hole in that area. One of the non-dimpled version has the vertical cut out area for the AC and the other one has the horizontal oval cut out area. The dimpled version matches up better than the non-dimpled pads by the holes that are in or not in the pad.