The RE non heavy duty uses a 3/4" heim (5/8" after a spacer thats included) parallel to the ground, single shear (the bolt is only connected to the mount on one side). The heim uses up about half of its movement just to angle down towards the axle, so you can't droop very far without maxing it out.
The RE heavy duty trackbar uses an aftermarket mount at the frame end, and a superflex joint mounted perpendicular (spelling?) to the ground, so its travel is only used "forward" and "backwards" as the axle moves - it will not limit droop at all.
At ~6-6.5" of lift, you use up pretty much 100% of the RE non HD trackbar's travel without drooping at all, and start overstressing the heim when you droop.
If you got it used, I'd buy replacement parts for it, new rubber bushing, new heim joint, new spacers, new bolt, etc.
1x RE1684 (hardware)
1x RM13010 (heim)
1x RM42000 (lower rubber bushing)
Keep the ones you take off as trail spares. I broke that heim once, before I changed out to a stronger setup. That's not to say its particularly weak, I beat the snot out of my jeep in 2005 and didn't do as much upkeep as I should have.. I've been paying for it in 2006.
-C