The 64 Mustang Electrical Assembly Manual (AM0003) page 24 shows the "corrected" routing. It's difficult to read, but the page seems to be dated 7 15 64. Both the 65 and 66 electrical manuals agree with the TSB change. (The I-6 is routed thru a cable strap on the shock tower but further back than the one shown in the TSB.)
Also of note, the 64 V-8 starter cable, C4ZF-14431-A (or -B) has one bracket attached to the right rear motor mount bolt, the 65 cable, C5ZF-14431-A (or -B) has two brackets, one at each bolt, and the 66 cable, C6DF-14431-A uses one bracket attached to the right front bolt. My 66 San Jose Oct 18, 65 build used the 65 cable. It was the original (made in Canada). I assume it was a matter of using up stock.
Jim