When building a custom brake system, make sure the master cylinder has the right provisions for disc versus drum brakes. Some systems use a check valve inline. Inline check valves are also available in the aftermarket with psi ratings for drum or disc brake circuits. Choose a master cylinder that is compatible with the type of brakes used at the front and rear of the truck.
Engineering your own brake system requires a thorough knowledge of chassis dynamics, including the vehicle weight at each wheel, the center of gravity and roll center, the force available with given rotors or drums, spring rates, the effect of lining choices, and a host of other concerns. If all of that sounds complicated, it is.
Another approach is to use every hydraulic and mechanical brake component from a suitable donor vehicle. If that sounds daunting, an alternative is a complete disc brake conversion system from a quality aftermarket source that has done the research.
In every instance, braking is a safety issue. Study OEM systems. The change from front drum to disc brakes requires the right proportioning or combination valve and the master cylinder designed for a disc front, drum rear brake system. Compare part numbers between the master cylinders, combination valves, and hoses of your truck and the donor prototype.
Where possible, use manufactured brake pipes with flare nuts already installed. When fabricating tubing, always use DOT-approved pipe with brake flare nuts. Double-flare the tubing ends. Aftermarket brake fittings and caliper hoses must be rated for brake use. Route hoses safely, clear of the chassis at full turn angles and extremes of suspension travel. Build a quality system that will match or exceed modern brake standards.