Questions on Liberty Rear disc on 8-3/4 per MoparAction Articles

I have the Dr Diff 11.7" rear disc kit in my '70 Charger.
The car stops no better than it did with the 10" rear drums. To me, the discs look better but offer no benefits unless you are road racing the car.
If you're certain that you want to switch to discs, the reason that they mention machining down that mount is to maintain the same axle shaft depth into the 3rd member to keep the axle shaft end play within factory specs. If you have non adjustable axle bearings, you can skip the machine work and assemble it all as it is.