This clip is Hardware Part # 356080-S32. Attached is a "cut" from the 1965 Standard and Utility Parts Catalog. This clip dates back to at least 1954 (the oldest Standard and Utility Parts Catalog I have), and to at least 1983, the newest one I have. It also shows up as this Part # in the 1965 and 1966 single year MPC's as well as in the 1960-68 MPC. Look under the Rear Brake Drum, 1126, and there it is. Also, the "-S32" is described in the 1965 Standard and Utility Parts Catalog as "Black or Zinc Chromate Paint".
I bought a dozen or so of these several years ago from Green Sales ; they still show about 1200 in stock if you're interested. However, please don't "buy them out" since, as I mentioned, they were used on all Ford cars going back to at least 1954, and I know there are others seeking them.
Hope this helps.
Bob