@fast_dave @rasouth @donalds
UPDATE: IT RUNS! I spent all weekend on the truck and every night last last week after work until late working, when finally at 12:30 am on Wednesday night, I finally got all the accessories buttoned up, oil primed the system without spark (was too lazy to figure out which was the fuel relay to pull that too), then fired her up. Came right to life, was rough, but on the next ignition cycle the idle was pretty decent. Plugged in the $10 amazon OBD scan tool and it heated up real quick to 195-205 degrees and stayed there. No check engine light, no codes. There was a pending EGR code for too high of flow but it went away now. I think that was solved when a vacuum leak from the EGR tube to the DPFE sensor was repaired (one of the original lines was cracked - new part is on the way).
Ongoing issues:
After the first drive, the clutch fluid was completely empty. I threw some new fluid in but that made the pedal start sticking to the floor, I'm guessing air bubbles got in. I tried to suck out all the air from the line I could with a turkey baster, then slowly pumped the pedal. I was worried I damaged something for a bit, but after a while it seems to engage/disengage just fine. Occasionally the truck starts a little rough, but has yet to fail to crank. There's an occasional slight stumble at idle, seems like a misfire (but not bad enough to trip a code), but I'm attributing that to poor connection between the plug wires and coil pack. I'll update once I get my shiny new NGK wires in from RockAuto and use electronics cleaner on all contacts and dielectric grease on the plug boots. One of the connectors to the coil pack is a little bent up and I think that may be my issue. Could also be a dirty MAF, IAC, many other things... We will see. AC doesn't work, which is a huge bummer here in the Texas heat, but I'm working on it.
Work Still To Do:
Replace idler pulley, belt tensioner, drive belt, all heater hoses and clamps, backflush heater core again, try to diagnose the AC issue (buddy has a manifold gauge), replace EGR rubber lines, replace / flush all fluids besides oil and coolant (including the foul probably original 21 y/o diff fluid, yuck). New tires are the first item though, so I can get it past inspection.
THANK YOU so much everyone on this site. I'll keep lurking the forums and chiming in where I can, though I'm still a bit of a newbie I think this was a good first step. Onwards to making this thing reliable and take a trip in it. The next big project will be sending me over to The Ranger Station, though, as I replace my 2.3 Ranger's clutch, pressure plate, slave cylinder, etc...... At least I can drive the explorer in the mean time.