I may be too late to be of any help, but according to my August 2002 copy of the EPC, Part No: YIB 100040 is listed as Hi-line navigation computer for Japan.

Looking in the Rover 75 workshop manual, it would seem that the European Hi-line system is different to the Japanese one in that there is an additional component called the VICS - Vehicle Information Comunications System. This is a traffic information unit which receives traffic information from the FM band and displays the info on the LCD. The receiver is connected to the navigation computer by a dedicated communications bus.

Also it describes the disc drive contained within the Japanese unit you were asking about as being a DVD-ROM drive not a CD-ROM one as used in Europe.

So it would seem the two systems are incompatible with each other if you were thinking of doing some interchanging between them.