You can buy disk's in Aus for $30 for cruiser or GQ so with the exchange rate that's what, 10quid.
It always makes me laugh when people say the are keeping it Rover and then proceed to fit MD's, Ashcroft KAM etc. They fit a rover housing but the are NOT rover. So the only bit that is rover is the housing, and generally that will have been strenghtened anyway.
A nissan GQ or GU/GR front diff will bolt straight into a RR/Disco/Fender using the Nissan lower arms, no mods to the chassis at all. You need to make up a panhard and steering arm but that's it. You don't even need to change the coil pads if you don't want to (I did personally as I wanted to run rover springs).
Pics of GQ front in my Rangie
For the rear is is better to run an 80 series than the GQ. Having run both in the same truck, and blown up 3 different tailshafts with the GQ, including wideangle uni ones. If it is just for a comp rig the GQ is fine, but if it is road driven regulary the vibs will annoy you. With 80 series rear, for the tail shaft is stock rover and just redrill the flanges. There is more work putting the rear diff in, but it is well worth it IMHO.
The other thing with the Nissan & Toy swap is you get 4.1's as standard.