my proportioning valve is built in with my combination valve, two reasons for moving m c 1- i think my m c may be bad and it is so hard to get to when adding fluid 2- i bought my booster from master power brakes it is a 7 in. now i find out it may be undersized so im using a 9 in. g m booster on firewall. should be finished with mods. sat. morning will let you know hayless