Heads up to those that install a 2 bolt aluminum master cylinder.
Thought I'd add my experience since I've got the same Dr. Diff setup as the OP - 13" front / 11.7" rear with 15/16" MC. When I first bench bled the MC there was absolutely no fluid movement out of the rear port until nearly half the piston stroke - the front port had fluid movement immediately when the piston was moved. I contacted Dr. Diff and he sent me another new MC. When I bench bled that one I thought I saw some improvement, but I believe the results were largely similar. Since I admittedly had no previous experience in this area I assumed the fault was mine and went ahead and installed it. This was last summer, and the car still has a ways to go before it will be running. If the ports are truly reversed that would explain a lot - I will be following this thread to see if more information on this comes to light.
Thought I'd add my experience since I've got the same Dr. Diff setup as the OP - 13" front / 11.7" rear with 15/16" MC. When I first bench bled the MC there was absolutely no fluid movement out of the rear port until nearly half the piston stroke - the front port had fluid movement immediately when the piston was moved. I contacted Dr. Diff and he sent me another new MC. When I bench bled that one I thought I saw some improvement, but I believe the results were largely similar. Since I admittedly had no previous experience in this area I assumed the fault was mine and went ahead and installed it. This was last summer, and the car still has a ways to go before it will be running. If the ports are truly reversed that would explain a lot - I will be following this thread to see if more information on this comes to light.