im just guessin here, but if they are bigger than the standard twin piston VT brakes you will need to find appropriate discs, and spacer shims (little rings that will prop the discs out off the wheel hub) new lines and that should pretty much be it.
keep in mind, changing your brakes will most likely create 'deep pedal' - i copped it badly with 330mm VE Brake Kit on the front of my VR. I still need to get a modified VT brake booster + master cylinder (you may have to do the same, depending on how bad it is)
94 VR V6 - No ABS & NO IRS... a true mans steed and a 99 VT XU8 for good measure.