Chris : Part of the problem here, that there is no info on this clip, is that it was not serviced (ie not available as a Service Part). I have attached the illustration from the "1965 Only" Parts and Accessories Catalog ; don't know if it shows it any better than what you have. The key here is the "star" shown by the Part Number. I have also attached what the "star" symbol means.
In the drawing, it appears that this clip bolts into the rear of the head. Does this make sense (I am not that familiar with 65 AT applications, and 1966 and '67 have a totally different clip arrangement) ?
As far as the "finish", a "Special" designation (usually S100) can designate anything not described by the other finishes, materials, etc. which leaves it "wide open". For this application, I would think it ought to be at least rubber coated, and possibly even a "spring steel" type with the purpose of reducing vibration, rattling, etc.
Just some thoughts.
Bob