Does your setup have the cable bracket, like the one below the right port, in the picture below?
If you do, then you can use the cable from a '75-'76 model (rubber bumper mk 3) pretty much out-of-the-box. I have one for my '74, when I get around to putting the engine in. Though for a '79, you may be better off using a mk 4 ('77-'80) type.
If you don't have this type of bracket, then Redline or one of the other Weber dealers online might have them available.