With the engine removed, it was obvious that the engine loom looked pretty sad. There was some cracked insulation, loose solder and melted insulation from previous shorting, while some of the original insulation had been replaced with adhesive electrical tape. Was this the original engine loom? It's hard to tell, but I suspect it was original, so possibly more than 50 years old.
I ordered a replacement engine loom from Zip Corvette. The looms they sell are made by Lectric Limited in the USA, and the quality is fantastic. There is no way your local auto electrician could produce a loom of this quality — every wire, connector and boot is identical to the original, right down to the correct fiberglass heat shield on the temperature gauge sender wire. Their looms are wrapped in OEM-style non-adhesive vinyl (not electrical tape) and they use the highest-quality automotive wire available.
Installing the harness was very easy, and the result looks brilliant. All the old wires that had been painted black by a previous owner (when the engine bay was repainted) are now the correct colour, and the insulation looks perfect again.