Original Cruise Control was Perfect Circle Brand (no longer in buisness). There is some usefull information (pdf format) under the files section over on the Yahoo site for SportsCoach Enthusiasts vintagesportscoach : Vintage Sportscoach Owners
You would have to join the site to gain access to the files. Once in the files section look for files that contain "Perfect Circle" in them.
The control box is most likely mounted on the drivers side frame rail. The vacuum hose from the bladder connected to the carb linkage, the wiring from the steering column switch, and the speedometer cable will be connected to it.