20s for the Demon - how low can I go? (big wheel haters don't look)

Rjsjea hit the nail on the head.
After doing some measuring, the sad conclusion is that differential clearance to the frame is a major limiting factor.
Lots of pics here, since there seems to be some interest.
I purchased a 325 50 15 for comparison since that is what I was considering before getting infatuated with 20s.

First are pics the way I would like to tuck the 325s if I were to use them. Hard to compare without a wheel, but I like that look a lot, even up a couple inches is nice. From the inside you can see it takes up all the space to the frame rail. Some trimming on the frame and fender flanges would be necessary. Lots of lateral room for the 275 45 20.

Notice in the side view of the 325 where the frame rail sits. This is the sad reality. I calculated that 5" is needed from the wheel center to the frame. The 8.8 diff is about 3.5". I rounded to 4", half of that is 2" plus a minimum 3" for leaf spring travel makes 5". The marker stick and a level were used to position the wheel with center to frame at 5". The last pic shows how this limits the tuck on a 20" wheel. The one before is the same process applied to the 325 50 15.

Rjsjea mentioned notching the frame. Not sure how that's done but I'll be looking into it as I don't care much for the look of either of them at that height. I'm not sure how coil overs can help this other than limiting suspension travel down to 2" or so. One inch gain is not enough.

I'm curious how others like swisswill have gone so low in the rear.