Thanks for all the help guys!
I wish I had read the last post prior to replacing the plugs, but anyways..this is where I'm at. Replaced the plugs/wires this morning. I didn't test for spark on all 6 plugs, which was stupid.. so I should do that. However, I'm getting a bad suspicion that the UIM is part of the culprit. When pulling the plugs out, I did notice some coolant around the UIM... so apparently it did start leaking. There was regular dirt/grime before, just from age, but this is the first I've seen the coolant. Also, when first attempting to start it this morning after finishing with the plugs/wires, I saw a small, white cloud of smoke come up from the engine. (Couldn't tell where from exactly, as the hood was still up). I'm hoping the engine hasn't truly become hydrolocked.
I can try the pressure test for the coolant still. Being an outdoor project, this is definitely taking longer than need be. I do have a garage, but it's not insulated yet...kinda of useless, right?