Nice...thanks for details
If you think about it, the factory put a slip joint/splines in the driveshaft. The transfer case/transmission is mounted stationary in the frame, the rearend is free to move back and forth in the truck as the rear springs flatten out.
Your bar is mounted stationary up front, but it's mounted stationary to the rear axle also. It can swing in a long arc, but can't grow in length when the springs flatten out. I know there are a bunch of them out on the road, and people seem happy with them, so they must work somehow but it makes you wonder about it.
Just adding a shackle to that setup wil render it pointless. To do the shackle you need to have the axle end mount at top and bottom like this. This is the bar I am using and it works great. For on road use I would use bushings instead of heims. It does clunk sometimes on mine.
http://www.ruffstuffspecialties.com...krLd_YFfCDkcfV1GYvu8xa0NTdEDybdqb0aAoSq8P8HAQ