Factory AC removed, no heat!

you can stake open the vacuum actuator for the heat control (heater control valve). Or just apply vacuum directly to it from the engine. I don't remember if it is inside the dash or in the engine compartment, follow the heater hoses into the firewall. The blower motor should be wired and works fine? correct?

what your looking for should look like this or simular. just a simple on off water valve that works from vacuum.
http://www.autopartsnetwork.com/1971-dodge-dart-hvac-heater-control-valve/avaagyCD5uTGJ

Or try to connect vacuum to the hoses you have going into the a/c /heater controls at the dash and see if you can get vacuum going to the valve. From what I see in the service maual the HCV is in the engine compartment so one of the two cut vac line you see one should go to it and the other would be engine vac going to the main switch.