Some master cylinders have residual valves built in.
From the factory the residual valve has historically been installed in the master cylinder. The proportioning and metering valves are downstream of the residual pressure valve; cleaner install. Some after market conversion kits have residual valve downstream of the proportioning valve. I doesn't makes much difference where the residual valve is installed. Make sure your mc has no residual valve if you elect to install one.
One advantage of installing a 10# residual valve for drums is the slight pressure will help expand the wheel cylinder pistons; minimizing leaks. Another advantage of the 10# res press valve is to minimize pedal travel.
A 2# res press valve for the discs is most likely unnecessary unless mc is lower elevation than calipers. Caliper pistons tend to stay in position w/o encouragement from res check valve.