what is the best way of getting the old one out and new one in? How much of the dash area do I have to remove if any?

Not sure which bit you're referring to, but this may help :- http://www.mindserv.co.uk/loom_replacement.htm

Im refering to the engine wiring loom

I'm not sure about RHD cars, but usually you only have to bend/grind (dremel) away the small metal plate , that fixes the loom going in the car, out of the way.

No need to remove the dashboard, because even by removing it, you still won't have access to this small plate, since it's behind the aircon stuff and you'd have to remove that also.

 

Once you have the plate out of the way and the old loom out and you are ready to put the new loom back, I have found it's best to get the big white connecter in first and the blue ECU connector in second...but it's a bit fiddly and you may have to bend the firewall around the hole a little.

 

-Eric