I have seen enough sierra wiring in the last 16 years to know that I would prefer a custom loom.
I can, pull and refit a sierra loom in about 4hrs though ( including stripping of interior trim
On the roadster there is really only lighting and feeds to the engine management loom to consider.
No electric windows, roof, locking, heater fan, courtesy ligh, audio, heated screens, AWS, bulb failure, imobaliser, abs, cigar lighter, front fogs, heahlamp wipers, dash dimmers, wipers, variable speed, door open warning, fuel computer, etc...
theres a lot to strip out, or a lot of junk left in.
TT