Yup. It is the front that seems to not get the pressure it should, but the rear might take mor too, if not the prop valv in the combination valve is just doing it's job and preventing the rears to lock up.
The combination valve came with the car whe I got it. I believe it was part of a complete Ssbc 4 corner sisc brake kit with a 2-bolt GM style Master cylinder and booster. Only thing left now is valvea and rear brakes.