From the assembly manual; the cable has a part number of C6DF-14431-A. My MPC does show cable lengths, but that number was superceded and shows a more modern replacement cable. There is wire holding clip with insulation, that bolts the the block.
Page 8 in the 1967 Cougar electrical assy manual, and page 10 in the 1968 Cougar electrical manual.
It's about 36 inches long. The cable goes from the starter solenoid to the starter via a support loop on the forward motor mount bolt that goes into the block. The cable from the loop to the starter was encased in asbestos tubing.