They say you can use the stock one and put a different Prop Valve in the system and use the stock master. I called Cass at Dr. Diff and he recommended the 1 1/32 Bore Master. I have manual 4 Wheel Disc. If you are going to order from him, call and he will guide you through what will work best.
You could trim a little more $$ off of my set up by not using the Proportion valve I am using.