Lots of good questions!
I will try and answer based on what I have experience with.
110 front rotors should work but you will need to adjust the spacing of the caliper, I've only done it with Disco stuff mainly because the vast majority of these conversions (over here) are done on Disco's and D-90's.
1994 and up Defender rear calipers should work straight up with Defender rear rotors No adjustment to the spacing "should" be required. I've only just obtained my first set of rear 110 calipers and have not had any time to "fiddle" these calipers are virtually unobtainium in the states as a wrecking yard item because no 110's with rear disc's ever came to North America.
In theory they should work better but I'll have to swap them out to tell for sure.
You can use a 110 Front hub but you will find that the bearing spacing is too wide. You can add a spacer behind the outer wheel bearing race or you can add a ring under the outside edge of the outer wheel bearing on the stub, I did this and it was only 'OK" In the end I changed it.
1994 (1993ish for RRC) and up is indeed the point at which all things become the same but shorter. What we call the ABS hub and stub has narrower spacing at the wheel bearings and a shorter stub. From here on it become the standard for all Rovers that do not have unit bearings.
The bolt spacing is different for front rotors, that said the factory bracket couldn't be used but you could fab up some based on factory brackets with the bolt spacing for the front. I suspect that the master cylinder woudl really need to be upsized to make this work but i haven't actually measured the volume of the fronts compared to the rear.
For those that have fab skilz and want to make their own: I have a partial drawing of these brackets, I will finish it up and post it in a format all can use (probably not metric though :) ) give a few days and we'll see how far I can get with it.. It's a bit chilly in the shop and I'm a wuss..
