The residual valve is supposed to work quite well, I haven't tried one yet as I need to replace the calipers to try and sort my ebrake problems. The proportioning valve will depend on how much power you get out of the new rears, mine are pretty well balanced
The problem I have with the ebrake is that the auto adjuster is quite coarse. When its just clicked over the brakes aren't too bad but as they wear I get a lot of pedal travel just before they click over again. The ebrake handle needs about 10 clicks to pull them on too as the leverage ratios are very different.
Tcase ebrake works the same as a normal shoe setup but theres only one and its mounted on the back of the tcase  the shaft is then bolted to the outside of the drum where a wheel would usually be. If you know what its like then that will probably make sense ÂÂ
Edit:If the residual valve is only needed with discs then why do Summit sell a 10lb one for drums? Is it supposed to replace the ratchet mechanism by only releasing  part of the fluid pumped in when you apply the brakes