You need to remove that trim before putting the unit in, and then put the trim in.
http://www.sau.com.au/forums/topic/190825-head-unit-removal/
The very first post is for the R34.
There shouldn't be a gap or any issues, as they are a standard size.
I saw the for sale pics a few months back, it was only a closed door respray. Engine bay was still white or silver or something. Still very neat and tidy though. Wonder how they were allowed those plates, usually terms like those get rejected.