I think the determination for one bracket or two depends on the cable assembly part number. If it's a C5xxx, it requires two, if it's a C6xxx, it requires one. The transistion date is sometime in late 1965 or early 66 and probably is plant specific. My 66 "K", San Jose Oct 65 build, had the C5xxx cable with two brackets. The cable assembly was made in Canada and the brackets and insulator (and woven sleeve) were part of the assembly and Ford service apparently did not stock them separately.
Jim