First of all, who is mapping it? I'm going to assume Niki / R-Tech here. If other tuner, then you will need to check their hardware requirements.
Secondly, do not fit the injectors unless the ECU map has been updated to suit - period. If you have to, do not drive it hard, or far, and ensure the MAF is unplugged - car will use the Lambda and correct as much as it can but this is not ideal and should be avoided.
Speak to R-Tech as you could send the ECU in the post and have a suitable K04 base map loaded on to suit the injectors.
When converting a K03 car to a K04, you need to remember the 3 bar MAP sensor (so the car can see more than 1.5 bar of boost) and the 200 bar rail pressure sensor. These are standard sensors on a K04 car. The K03 has 2.5 bar and 150 bar sensors respectively. Some tuners (such as Revo) make do with the original sensors but Revo will not push the limit of your K04 converted car. Double check with R-Tech but I'm pretty sure Niki will want the K04 sensors on there
As for the N75 - If you unplug it the car will be in total limp mode due to an N75 fault/short to ground fault. If you connect a spare/second N75 electrically (only electrically - not plumbed in to the vac pipes - leave these as they are) this will allow the car to run on actuator pressure.
If in doubt, speak to your tuner and ask their advice
yes I'll be going to niki for this and no messing around he knows his stuff.
I was thinking of fitting it all up and going driving down to niki around 80miles from my home. Is that a bad idea?
I'll give niki a buzz and see what he says as it's better to be safe than sorry.
Right now I understand you
get a secondary N75 and just plug it on electronically
I've still got a long way to go in parts yet, S3 injectors on their way.
Now I need all the ancillaries gaskets DV relocate pipe etc.
You've been very helpful as this is the first time I do something like this so all the help is very much appreciated and maybe one day we can all get to get here and have a laugh about it
will be doing more show visits when the beast is ready that's for sure.
Thanks again