Hey Gerald, yes heck these guys can go on hey? ;)
Salisbury diff is a Dana 60 made under license in the UK after WWII. Big round pumpkin housing, so the guys "shave" it by grinding off as much material as possible to get center clearance.
R&P is Ring and Pinion gear set, the two bits that define and set your diff ratio.
As for disks versus drums on the Mog Portals: the Mog drum brakes are able to stop up to 17 tons. (The SADF Buffel was a V-hull, mine-proof, armoured personnel carrier bin body mounted on a Mog rolling chassis. I drove in those enough times in my life to tell you they stop pretty well).
With a decent brake booster and master cylinder, I wouldn't have any worries with them stopping a little old Land Rover.

