Vintage Wiring Harness, Ringwood Vic, have a lot of wiring items and the outer fabric conduit that is impregnated with black stuff (don't know if they still use tar these days).
http://www.vinwire.com.au/
From a maintainability point of view, I would use red for positive cables and black for negative cables. As suggested, heat shrink can cover the ends.
I would make the cables to suit, don't go off the parts book. Often during the war, materials were in short supply so they skimped where they could. Now days a couple of extra inches will be useful.....