The Threaded one is the output port.. the other two are return port to the reservior. This pump most like was from a Hydro Boosted truck. If you are not using the Hydro brake system, use the lower port for the return and cap off the upper one.
71' Chevelle, 99 LS1/Viper T56,Full Hotchkis TVS,Custom Cowl Induction CAI
84' Z-28 350/T5
88' C4 Coupe L98/A4 71' Nova - LS1/4L60E
, Full Hotchkis TVS Suspension
79' G-30 SWB 4X4 Van, 400cid / TH350 NP205
48' Ford F-1 1/2 Ton Truck, Stock 6cyc/3sp