There are a couple reasons (perhaps more?) why you might need to adjust the drag link after installing the track bar bracket. There will be slight length differences in manufacture of the 3rd generation bar. There will be slight differences in how the bracket fits your truck vs. another. (According to what we've heard from Marv and Darrin, there may be more difference in this than any other factor. ) And there could be differences in the existing configuration of your specific front end geometry. Combine all this, and you'll probably need to tweak your drag link to center the steering wheel.
When I installed the track bar bracket, the new bar was about 1/8-3/16 inch short of reaching the pivot bolt on the bracket. I turned the steering wheel enough to move the axle so I could fit the bolt. And, from my test drive after the install, I needed to shorten the drag link - just about a half turn.
As you'll find on other threads, the issue of centering the axle is sort of a moot point. The axle can only be centered for one point in the suspension travel. And ONLY for that one point. The issue just isn't that critical. What is critical is that the bump stops contact the center of the axle pads, and changing the track bar length a lot will prevent that from happening, if you ever bottom the suspension.
Hope this helps,
John