Unless you are installing race style brakes with separate front and rear masters and adjustable bias comtrol and proprtioning valves, you should leave the stock combination valve.
20k mile '80 Malibu, currently undergoing long
term (aka no money) factory style install LS6 454, Cowl Induction, Legend LGT 700 5 speed. Full Global West suspension, 17" N90 wheels, 12" front/11" rear disc brakes, 9" 3.70 Auburn Pro posi.
"The older I get, the faster I was"