There's been a lot of discussion over the years regarding residual valves. ECI and Master Power Brakes will tell you to use residual valves when the MC is located under the floor. I have 2 trucks with the MC mounted under the floor and I use no residual valves. I have a '54 Chevy panel, power brakes with disk brake front and drum rear and I use a proportioningl valve. I built this truck 19 years ago and the brakes work great.
I also have a '48 Chevy pick up that has a manual MC ( '69 Corvette) and drum brakes front and rear. I put the residual valves in and experienced a poor brake pedal. I took the residual vales out and replaced them. Still a poor pedal. I replaced the residual valves for a 3rd time, still poor. At that point I took the residual valves out and the brakes work great.
