I know nothing about either of the looms you mention but at the end of the day all you are looking at is connecting bits together. If the CX has enough cables and in the right places it could be used so long as the rating of the cables is right. Unless your friend is going to draw out the new loom as he goes along it could be a nightmare in the future tracing faults.
I would have thought either get a GS loom or rewire it from scratch would be a better bet. Wait for some of those who do this to answer you first though