Hy HFfarms, I am a mechanic, not an engineer and I don't profess to be one. The fact that I have never seen this brake line plumbing system until you showed us your trucks system sets a red flag in my head. Over the years there have been many different things tried in the field of vehicles, some ideas were good and have continued and been refined and improved. The fact that this particular system was/is not in widespread use tells me it was not something that added a benefit to to the more common single application to the brake booster system. As I said previously, if it were my truck I would remove the second output line from the booster back to the master cylinder, plug that port on the booster and run the system with one output from the master cylinder and one output from the brake booster to the braking piping system. As that is the system we are more used to seeing in a single braking system I think it will work fine. It is your truck and you may restore/rebuild it as you see fit, please verify that whatever system you decide on is safe before you venture out onto the road.
