The power feed should be through a fuse from the ignition switch "on" position. The shop manual has a wiring diagram which shows all the components of the electrical system. The Saganaw OD trans was available from 66-69 - so you have a later power train which is good. 1st gear is syncro.
Fred


1956 3100 Pickup/Red/350/3sp OD/PS/Disc Brakes
1957 Bel Air Sport Coupe/Red/355/TH350/PS/Disc Brakes
2017 Silverado LT Single Cab SB/Black/5.3/6 Speed Trans
1947 Willys CJ2A w/F-Head engine