Saw a neat trick over on the Speedsterowners board: Lay out your wiring harnes on an actual piece of wood, close to the length you’ll need. V in some nails to keep the wires straight and mark all your terminal ends where they go. That way you can get the harness built on a bench, instead of lying on your back with your head under the dash.
The guy who showed this used a terminal block (any boat supply place or Radio Shack has them) to keep the front and back halves of his harness separate and manageable. Put it in next to the fuse holder. Used zip ties instead of electrical tape or a split loom cover to keep everything tidy.