I'm running the stock cables on my Explorer disc kit and the cable clamp trick worked fine, except I didn't fold the cable in half, I used the "u-bolt" piece of the clamp in the brake lever notch, then layed the cable in the ubolt parallel with the lever and then screwed the clamp together.....no issues after 2 years of use.....but what I've found is that the 89 XJ park brake lever doesn't have enough throw to engage the e-brake firmly. The rig will still move with the e-brake lever pulled all the way, which I have not been able to adjust to correct.
I doubt this is cable length issue, more a lever travel....I've toyed with ideas of a cam mod to the lever, or mid linkage, that increase the throw, but haven't devoted much time to it. I need to resolve this, I may really need the e-brake sometime and not have it.