I can't remember if I brought this up in one of the previous threads on Styled Steel Wheels, but in any case, it is something to ponder..
In the 1965, 1966 and 1967 individual year MPC's (Parts and Accessories Catalogs), each has a listing of wheels that were available for that Model Year. The listing shows applications, size of the wheel, number of lugs, lug bolt spacing. etc. Specifically the columns shown for each wheel have the headings of "Model", "Part Number", "Qty Per Vehicle", and "Description". In every case, the "Qty Per Vehicle" for Mustang Styled Steel Wheels is shown as "5". While MPC's are generally considered "Service Part Oriented", the question remains, why would "5" be shown when if a person only needed one to replace a damaged one, it could be purchase by "each" ?
Another interesting little "tidbit", is that in the 1965 and 1966 Ford Accessory Catalogs, the Mustang Styled Steel Wheels are shown, and priced as a "Set of 4", ye t in the 1967 Accessory Catalog, they are shown and priced by "each".
Just a little more to think about on this subject.
Bob