15/16" MC with 2.75" calipers any problems with stopping ?

Residual valves were installed to keep the wheel cylinder rubber cups in contact with the cylinder wall, preventing leakage.
Newer W/Cs have a spring with a "spreader" to mechanically hold the cups against the cyl wall, no need for residual valves.
If you know your rear W/Cs have the spreader spring, no residual valve needed.
Not sure, - or no spring, install the R/valve .
The residual valve will have no effect on W/Cs with the spring .