True, a black engine bay can suit Zed's with the 70's race, JDM, flares look I reckon. Good solution with the loom, you can probably get away with that, the problem is those lines... nobody would argue that replacing them is a good thing, it just increases the scope of the job a little (if you have a white engine bay like me )!
Just an idea: have you thought about the speedo cable route... It goes from speedo, through to engine bay and then back along gearbox. If that cable could run up through the transmission tunnel somehow (maybe through inner shift boot...maybe), that would be one less cable in the engine bay for a pretty easy re-route?