Generally (if not always?) the front brakes go to the end of the master cylinder farthest from the brake peal.
If you use the standard GM proportioning valve, visually divide it into two halves, the front brakes have two outlets from the valve, one at a 45 degree angle up, and one down, and the inlet for the front is on top close to these. The rear only has one outlet and it points straight back, the inlet for the rear in on top near this.
Grigg
