Based on the article above, those of us putting an 8.8 with discs where there were drums should be making sure we have no residual valve. I've read everything I've seen on the 8.8 swap here and not seen this discussed.
I agree, because if I remember, the residual pressure check valve is needed to keep aout 8-10psi on drums to prevent dirt and debries from entering the brake system through the wheel cylinder.
I was once considering an 8.8 swap and retaining my front drums till I can afford a BBP disc swap.
To do that, I would need a an inline proporting valve (adjustable) to control brake bias, as well as an inline metering valve to keep the discs from activating untill sufficent pressure (60-80psi) is on the drums to overcome to springs to prevent the rear wheels from locking up under hard braking. Lastly the MC would have to be changed because on vehicles with 4-wheel drums, the residual pressure check valve is built in to the master cylinder and the residual pressure on the rear circuit would cause the brakes to drag back there.
Moreover a vehicle considering this swap with front disc brakes, adding the 8.8 with discs to the rear would eliminate the need for a residual pressure check valve as well as a metering valve. The only thing required would be the adjustable proportioning valves on both circuits.