Hi Chris
I built the OE loom from a complete but very tatty VX Loom. Measuring and noting the wires by colour I then ordered thin wall modern cable using the fact it caries more load for its size to fix OE design issues. Finding the colours involved multiple suppliers, but only 2 substitutions.
I swapped Tape for cable ties at key junctions and made it one wire at a time end to end each loom sections on a large IKEA table. This was after Auto Sparks sent it back as too difficult for them!
I used modern sealed connectors in vulnerable spots in the engine bay and Red thin wall in place of black and white for the fuse box feeds. NB Junior Timer sealing boots replaced the rotted OE rubber boots.
The ECU and additional fuse box wiring is in a large Excel because there is no OE Wiring diagram. Drive By Wire, Sequential Injection, Cruise Control, Knock Control and on Board Wide Band Lambda took me beyond entry level ECU's
So much time is lost working out where to run the extra wires.
Eric