Yes keep the front of the master to the front brakes ,on my 52-3100 the master installed with the front of the master facing to the rear of the truck , I don't know how the master is mounted on a 56 GMC ,I used a 67 C10 master because the 67 had drum drum brakes. You could use a 67 C20 master just check and see if it's drum drum.
Pete
