May I suggest that you get a set of Mustangs Assembly Manuals for your year Mustang. There are several "grommets" listed and most seem to be from other year and model Fords.
Jim
Since I'm not working on a 68 (the focus of this thread), I have no desire to assume the grommet is the same as the 67 that I do own but deductive reasoning suggests it IS the same, I do have the full set of Assembly Manuals for my 67, as well as a printed copy of the EXCEL hardware sheets you have provided (available in the site's Library section ~many Thanks Jim). I have these printed EXCEL spreadsheets sorted both alphabetical as well as numerically to exclude (as much as practical) options that do not apply to my specific project (the EXCEL program has excellent sorting features)...all of this was a HUGE asset in the final assembly process, especially with having the AMK paper catalog alongside. May every member of this site do likewise for their build.
Ford part number should be C4AB-14603-A for the grommet.
Yes, that's the same grommet number. It is made out of unobtainium in NEW form. The only source I am aware of is 1960's era Ford products that have a trunk light option. (again, a person can now search the FORD Master Parts Catalog aka the MPC, using the C4AB-14603-A number and find all other applications where it can be found in the wild...hence the initial reason I suggested adding mention of the grommet to this particular thread).