Determining the Ford service stock number would be the first step.
Jim
This is turning out to be quite the challenge. From what I observe:
1. The 1967 catalog lists C5ZZ-2082-C for the right, and C5ZZ-2082-D for the left.
2. The 1979 OSI says that the C5ZZ-2082-C replaced the C5ZZ-2082-A. My guess right now is that this was done at some point during 1965 production. The C5ZZ-2082-D was not replaced.
3. However, the 1960-68 MPC lists C5ZZ-2082-C for the right in concurrence with the single year catalog, but in the illustration section identifies a 2A056 for the left.
4. There is no 2A056 listed in the text section. There are none listed in the OSI.
5. On to the 1965-72 MPC, which a 1961 Thunderbird bracket for the full 1967-70 Mustang range. Things like this are not rare in this version of the catalog, which is why for me I only use it as a last resort.
6. I found a picture only, no bill of materials, in the chassis assembly manual on the "brake" page.
7. The shop manual rarely lists part numbers, and I would hazard to say "never" for something like this, so I did not look.
I'm running out of material here, will look for more later. If anyone has the answer please chime in.