This item caught my eye. I tried to repair this trim piece on a friend's 69 Sportsroof. It was shattered into 3 or 4 pieces. I used a special epoxy I got from Tap Plastics that was formulated to work on formed plastic parts that had a mold release incorporated into the plastic material prior to it being formed. Almost any other epoxy would not stick. I did get it fixed. A few years later, my friends son took out about 75 feet of chain link fence on a frontage road parallel to US 101 with the car.
I think i found the aftermarket piece in the NPD catalog as their stock number 31490-2A. That's for the right hand side. No left side part was listed. Interestingly, only the right hand side is listed in the 75 edition of the MPC, C9ZZ-63311A92-A1A. As there is no 69 Mustang Interior Assembly Manual published, the MPC is the only source of information.
Jim