Sorry, the last picture with the skid plate will make it more clear, I'll get that tonight (It was dark when I finished and I didn't get a picture)
Maybe this will clear it up
Stock height 8.25- self explanatory
6 inch lift with 8.25- Drops the diff 5.5 inches from stock (along with the front and rear cross members as can be seen- thus keeping the stock CV angles while allowing the truck to be raised 5-6 inches) IE the bottom of the diff height is actually the same height or close as it is on a stock height truck, however obviously, the rest of the truck moves up. IE center axis of the diff is the same in respect to the wheel.
6 inch lift with 9.25- The diff sits at the same same center axis as the 8.25 with six inch lift, however since the diff is bigger the lower edge of the 9.25 is probably .5 inches lower than the 8.25. However the bottom of the diff still higher than the skid plate, so no loss of ground clearance. The steel bolt-on diff mount from the lift kit (for a 2500 lift) puts the mount at a lower place than the 1500 lift kit mount for whatever reason (I think it's because of the size of the 9.25 diff doesn't allow the mount to be directly in front as there would be no room, they had to put it lower so it can sit closer to the diff.... )This is why I had to reweld the mounts, however the diff itself is at the same (or within .25 inches) same center axis.
Let me know if that make sense. The picture with the skid plate will probably help.... My bad.
EDIT- Also after saying this. Might be interesting since, I believe the cross members on a 1500 and 2500 on the lift kit are the same width, possible sourcing a 2500 front cross member, with the proper spot for the front diff mounts, may make this bolt on to a truck with a lift. IE only parts you would need are 6 inch 1500 lift, and then the front cross member and the bolt on steel diff mount from a 2500 of the same brand lift. Would be interesting.
Also- the trailing end of the diff plate bolts to the "stock to the lift kit" location on the rear lift kit cross member