Hello Steve,
I like all-year Mustangs, even the Mustang IIs, so I'm not picking on any particular year! But you have to be a member of the '65-70 club to get any respect from the repo people!
The name for the filler panel in Ford speak is "Filler, rear floor to quarter panel." The filler panels followed the two-year styling cycles on the Mustangs '65-66, '67-68, and '69-70 rather than trying to get one panel to fit all those years. The '65-70 Mustangs all had trunk mats, so it was not like the filler panel was visible so that everyone would see any imperfect fitments.
It appears that Ford only utilized the filler in '71 on our Mustangs, as there are no listings for it in '72 or 73. That may explain why the repo people are not interested in us on that part.
It also appears that Ford only used them on the left side in Mustang applications. Since the taillight and fuel sender wiring was in that area, it was probably used to protect those wires. I remember there was only one on the driver's side of my '67 Mustang.
There probably wasn't a great demand for these fillers since all the Mustang applications, including the D1ZZ-6511228-A for the '71, were discontinued by '77.
Your options are limited to getting a previous year to fit or mocking a cardboard template and then transferring it to some fiberboard. Sorry. I wish I had better news for you!
