Have seen two variations, not sure if either is correct.
One is a small "C" clip on both rods, near the middle, not attached to anything. The other is an "M" shaped retainer screwed to the underside of the deck between the trunk lid and rear window clamping both rods to the metal in the middle.
Have also seen some with a spiral "hose" on one rod. Some none...
What is correct for a '68, and does it vary between early and late, or by body style (I have a convertible and 3 coupes). San Jose (early convertible, early and late coupe) and one Dearborn (late).