So you are about a differential locker in your 1979 CJ7. Are you talking about the front diff or the rear diff? If one of your diffs has a locker in it, it isn't OEM -- it's aftermarket.
I don't know of any differential lockers for CJ7's that are vacuum operated. There are ARB Air Lockers that can be obtained for either front or rear differential. But those are air pressure activated, not vacuum activated.
You'll need to find out the brand name of the locker that's in there.
1977 CJ-7, fiberglass body, AMC 360 w/ headers, DUI ignition, Edelbrock intake and Holley 4150 carb, TF999, Dana 300, 4.56 gears lockers, York air comp, 4" susp lift, 2" body lift, BFG 35" M-T tires, Megashifter, AGR pump & box, REP8000 winch.