Re fuel injectors cutting out- examine/clean the injection trigger points in the distributor. They are located on a tray that slides in below the ignition control, and these points can eventually become oil fouled.
The ECU is in the passenger side footwell bolted to the firewall.
I don't know where the vacuum actuator for the cruise control is. The hose you describe sounds like vacuum that opens and closes the passenger side damper for the climate control system (for exterior/recirc air).
Hope your cruise amplifier works. I wouldn't know where to begin to get service for those old Philco units. (Anybody know?)