On my '75, the vacuum source is on the intake manifold directly behind the carburetor, sandwiched in between the carb and the distributor. This is a threaded 'tree' that has two vacuum outlets, one of which goes to the tranny and the other to the vacuum accessories.
Mine is the same with the hose running to the vacuum port on the intake manifold off a hard steel line from the modulator. The hose is used only on the ends. The other port on the fitting feeds the vacuum tank.