With most of these Conversions, I think you'll find that they fit up matching rear diffs to what ever the lump is that been fitted up front. They do this mostly to be sure they have matched ratios at the front and rear axles, as well as it being up to the task of what ever the power output is. If the ratios between the front and back are not exactly matched it would not only wear the viscous clutch prematurely, but also cause it to handle and drive like a dog.
I've look at a number of the conversions over the years and most of them are a work of art, really awesome ideas and engineering have gone in to them, and I really respect the guys who dream them up and build them, however - and this is only my own personal view - once you slip stuff like this in to a Mini, in particular that rear suspension set up, it's no longer a Mini, eg, that one appears to be a Honda CRV AWD, just with a Mini Body Shell on top. Awesome job, but no longer a Mini.