I can recreate the clunk by hand by rotating the front drive shaft through its radial play, so I'm confident that loading and unloading the drive train (via tapping the brakes) would do the same. As for the clunks caused by bumps, it clunks quite a bit by pushing it up and down (lateral play). I'll see about taking some video of this play.

At any rate, I'll know soon enough. In an effort to continue to throw money at this problem and single-handedly stimulate the economy, I'm picking up a front drive shaft today which by some miracle is in stock at a local parts store. The diagnosis procedure in the TIS is pretty clear about the u-joints not having play, so may as well replace this thing to see if it helps.