How easy is it to swap out the instruments from a 98 car, with white dials and an electronic speedo, for those from a version 6 STi?

Anyone done it? I gather the STi ones have a centre diff display, but apart from that, is the wiring the same?
Plus will my odometer fit the new set, or will I be stuck with whatever the new set one says? I ask, since mine is nearly 11 years old but has only done 83,000 miles.