Unfortunately not many tuning/styling options are available for the 600. I know GMax made a set of lowering springs (I've still got the complete set in boot of my car waiting to be fitted. Only been there two years !!). Some say they are quite crashy though.
The Rover 600 is essentially the same car as the Euro Gen V Honda Accord (this article on it's development maybe of interest: http://www.aronline.co.uk/blogs/cars...pment-history/
So anything that fits that generation of Accord will fit the Rover.
The equivalent US generation Accord IS
different to the 600 (though wiring seems to be the same). Some accessories will fit, some won't.
I don't know which version of the Accord was sold in NZ.