I have updated a little ... again changing things when I think more about it in place rather than setting it all out first.

I have lengthened (or freed up) wires so far for the engine ECU and the igniter

Engine ECU going under passenger seat (this is where Nissan mount it in many cars including the EXA)
Igniter going on passenger side strut tower
Auto ECU going on passenger side firewall between heater and windscreen wiper

so with 20:20 hindsight I would set all the wiring out and eliminate the redundant plugs/wires and shorten the loom to fit nicely.... I love 20:20 hindsight