For UK cars or cars which would have been wired in England, Autosparks have very good looms made from old Lucas patterns. I have fitted a couple of cars with their looms and they have been pretty good. The main sections of UK-wired cars were cotton braided rather than tape, although some parts of the underbonnet sections were black taped. Autosparks supply all components for the harnesses, connectors etc.
From other responses I'm assuming cars delivered to the US did not have harnesses fitted, which surprises me as I had always thought these cars were pretty much complete apart from the drivetrains.
Roger
Autosparks, World leading supplier of classic car wiring looms