cable driven Tachometer and speedometer

The inner cable is most likely the S.S. White style. Every truck manufacturer pretty much used that style. Stewart-warner will replace it fine. The only difference are the cable windings are a different pattern. ( that is only a concern to someone wanting a concourse type restoration) The inner cable should pull out of the outer cover from which ever end is larger. Grab that end with needle nose pliers and twist and pull gently. Those cables wear and stretch and cause the needle jump so it would be best to just replace the whole unit. They come prelubed.
If you go that route. I recommend having the cable built a little longer if it seems like it is to short. You will know what I mean when you get in dash to remove it and there is not enough slack to easily and comfortably unhook/hook it to the back of the gauge. Longer won’t effect it. Cabover cables were 12-15 ft long doing the same thing.

 

Those guys know their stuff. They have serviced all the truck dealers and shops for years. They even have marks on their driveway for speedo cal. They know what box you need just by the rotation of tires and driveline rolling thru that distance. Tell them what you have that the cable is hooking to. Engine, trans and gauge. They should know. You just pick the length.