The plot thickens: I pulled the pass side valve cover and, lo and behold, the rear guide is intact and doing its job. I need to check the front cam guide, but boy am I tempted to try to fix these things in the truck and just button it back up w/o pulling the engine. Things looked really clean under the valve cover.
Oh, and adding to all this: the motor I had found locally turns out to be from a RWD vehicle (no balance shaft), and when I checked the VIN from the Explorer it's coming from, I discovered that in 2013 the mileage was at 155K -- that's 3k more miles than my current engine. Not sure it would be worth swapping.
Man, I am kind of stumped. Sort of tempted to try fixing what I've got and take a gamble... maybe swap out the oil pump too, if it's not a real PITA.