Christian,
Yes it is a single din size and it fits in exactly the same as the climate control in the GTS, it could be possible to make up a bracket either side for it to mount it below the climate. The best way would be to find a GTR climate control head unit to mount under it.
The whole thing can be disassembled to remove the guages, but the replacements will need to be less than 2". I was looking to do the same with white face autometer guages but the nearest size is 2 1/16", if you don't mind them sitting out the front a little, they might fit.
The reason for selling is that insurance is just around the corner, only if I can't offload the car to a good home first.
Ed