Hy Locust_Cutter, welcome, unfortunately the mid to late 60s were a time of change in braking systems for the larger trucks. Some were single systems with boosted masters mounted on the firewall, others were dual systems with two frame mounted hydrovacs, or single masters with a single hydrovac mounted on the frame. It can be very tricky trying to determine what is correct for a given brake system during this period. When you get back to the truck, have a good look at what equipment is on it, then you can tell us, and ask your questions with more information on what is on the truck now, hope that helps.
