Here’s another Mustang part that needs to be considered for reproduction, the push nut used on 65 to early (midyear) 67 Fastback trunk torsion bar right hand end, p/n 380264-S2, 1/4 in id, 3/4 in od, 0.025 in thk (measured), with 8 serrations for retention, see AMK Products Guide to Ford Fasteners 1955-73, pg212, p/n 380264-S.
Some history of my search: I found a busted one in the trunk of a 65 Mustang that was in a local Mustang shop yard. The only info I got from the part was the manufacturer’s name, PAL. I did an internet search and found that the company is now Tinnerman Palnut and found a similar item, T99220-171-4 in their on-line catalog. It was close, it had every dimension but did not use the serration retention. The sale representative (a friendly sales rep, he had a 69 Mach I) sent me samples, an installation tool and I cut the 8 serrations in one with my Dremel tool, painted it and installed it on the car. It looked good enough that I made several more.
Now for the bad news, that part is no longer manufactured, stocked or available.
A picture -
Here is Oct 1964 SJ
Jim