On the cars that I work on, the front brake line is attached to the port nearest the pedal plunger, which is the back port on a firewall mount. I installed my under floor ones the same way. The plunger points to the front of the truck, and I attach my front line to that front port.
1950 GMC 100 Panel Truck, 1958 270,
3-spd Saginaw with BW OD,
3.73 12 Bolt Differential from a 1966 C10,
Front Disc Brakes
Hill Holder
Bought it in pieces 9-1976, driving since 6-1978
Follow in the DITY 
