I am almost done with my brakes, and CPP provided cables, however I had to order custom cables. The one they sent me for the passenger side was just too short to make work, no matter how hard I tried. I too have a 68 with staggered shocks.
After looking at your pictures, my only guess is that the long cable is intended to replace a portion (or all?) of the front cable??? But like the post above said, it would need a threaded end for adjustment and doesn't appear to have that.
I called CPP about the measurements of the cables I should be using and they provided the following information
40 1/4" total length cable
31" casing (drivers side)
31 1/4" total length cable
22" casing (passenger side)
So my supplied cables are close to the same and tie in to the front, already existing parking brake cables.
Like I said.... Unless there is some magical secret, the passenger side is too short. The driver side is also plenty long. I ordered new cables and added 4 inches to the passenger side. Finally getting the project wrapped up.
That short cable with the casing looks like it might be the drivers side that hooks to the caliper, but I'm at a loss in the long one. And I'd say you are missing the other side that hooks to the caliper (depending on the length of the short one with the casing... I can't tell which side it would be.)
Hope you can get this figured out. Good luck.