As HanksDeuce pointed out, with hydroboost the brakes get high pressure first, giving them priority. However, what you shared a picture of is one of the Bosch Hydromax units. They are similar to the hydroboost units but they are bigger and were used on medium duty trucks instead of pickup trucks. They also used an electric motor as a backup in case the engine stops running, where as the hydroboost has a hydraulic pressure accumulator vessel.
On the two donor trucks I have dealt with, both mid 90's Ford F700s with 6bt engines and Hydromax brakes, they actually had separate power steering pumps for the brakes. The gear driven pump drove only the steering gear, and a separate belt driven pump drove the Hydromax system. I'm not sure how much of a performance impact you will see from using a single pump to supply both systems, but I am guessing the extra hassle of having two power steering systems was done for a reason.