The vacuum line is pretty obvious, the cruise actuator is the only thing under the drivers side battery. Just follow the throttle cable from the injection pump that heads toward the firewall then makes a u-turn back towards the battery, the vacuum hose and actuator are at the end. I would attach your needle valve a foot or so from the battery to make it easily accessible.
I restricted my cruise vacuum line with a barbed hose coupler full of glue with a pin hole poked though it. Gained around 1. 5 - 2 mpgs in cruise or about the same mpgs as driving by foot. Cruise is slow to get to the set speed but the throttle holds steady instead of constantly moving like it did in cruise before the restriction.