flow restrictors look like this and screw into the pump where the pressure line attaches. mosty used for rack and pinion applications where a gm pump is used on a ford rack. not sure what the cpp box pressure is supposed to be.
https://www.jegs.com/i/JEGS/555/60791/10002/-1
what kit do you have, the box mounted on the outside of the frame in front of the tire or the box mounted inside the frame where the original box was mounted? also, what pump do you have and what is the pulley size? does the pump "buzz" or whine when it is running? that is an indicator of a pump that is starving for fluid or has air in the fluid. sometimes turning lock to lock and then shutting it off and walking away till morning will allow the bubbles to find their way out. that is the ling method because it may take several of those lock to lock turns to flush all the air out of the box.