Ok. I went to sleep, woke up, had a good breakfast, and then referred back to this thread, the link posted by boogieman, and the FSM and I believe my crisis has been averted. What I ended up doing was removing the zerk fitting from the drive shaft, which relieved enough pressure to pry off the drive shaft so I could essentially start over and get my drive shaft "back into phase" so to speak. I followed the advice in the thread linked to by boogieman (thanks again man) and reoriented the two halves of the drive shaft so they looked as they appear in the FSM below.
Once I had everything back to normal, it was a simple matter of reinstalling the zerk fitting, popping in the drive shaft (which was much easier after removing even more grease), and reinstalling all the nuts and bolts. I took it out for a quick shakedown and the vibration at speed was completely gone as was the growling/grinding sound I was experiencing before, so I'm confident enough that this was the root of all my issues. I'll make sure everything is torqued down properly after work and then I'll put some miles on it and see what happens.
Lessons learned here: 1) Don't put grease through a zerk fitting with the shaft out of the vehicle. If you have to do so only put in one or two squeezes as opposed to the 6 or 8 I did (seriously didn't think enough grease could even pass through that tiny fitting but oh well). 2) READ AHEAD if you have a FSM, as a couple of pages after the first image I saw this:
Which would have at least prevented me from freaking out as much as I did. Thanks again boogieman for the knowledge, hopefully someone else sees this thread before they make the mistakes I did so they can save themselves the time and aggravation.