Nah, to install the HUD you just have to replace the instrument cluster with a SSS instrument cluster and connect up the HUD display unit. That's without the wiring problem...
I wouldn't know where to begin if I decided to replace the loom, same applies for splicing, I have an idea of what needs to be done but I wouldn't do it as i've had little soldering experience.
Has anyone here ever replaced a dash loom that may be able to give me a hand?