I'm putting together a 1970 Dart GT with original Kelsey Hayes power disc brakes. I'm using a stock type booster with the big bracket set up. I can't seem to locate the right hose for vacuum. 3/8 seems too small and 1/2 inch is way too big. I just got some 15/32 from NAPA, but again seems too big. Local parts stores seem unable to look anything up... Can somebody tell me the correct size and perhaps a source for it?