British Wiring sells poly sheath in various diameters. That's what I used when I wired my A65. The only downside, if you can call it one, is that the wires have to be fed through the sheath before the terminals go on, at least at one end. It just requires some planning and careful measuring. It's not original-looking, but it is tidy. And, if you need to make repairs down the road, individual wires can be pulled out and replaced if necessary.
+1 for the poly sheath. As mentioned, it does take some planning. I lay out the wires on the bike and cut to length (always leave an extra inch until you put the terminals on.)
I like to use Japanese brass connectors, better strain relief, and a proper crimping tool costs half as much as the Lucar tool. They also take up less space.
I just rewired my Trident and changed to a regulator under the seat, obviating the need for the long hot wire to the Zener under the headlight. At least I could leave the wiring for the Tri Spark as is.
Between the wire, connectors, and sheathing I probably spent less than $50 for the new harness. I'm retired so my time is free.