The tiny "kitten" turns out to be a four-year-old male, according to the vet, based on his teeth. Alpo is horribly malnourished after living in the wild for a long time, but is otherwise surprisingly healthy. His legs, his teeth, his ears are fine; normal temperature. They gave him his shots, and had to shave off almost all of his fur (due to serious matting and fleas), so he now looks even more scrawny, but he'll fatten up over time. Unsurprisingly, he's been eating like crazy. Our suspicions about human contact were correct; he's already been neutered and (unfortunately) declawed. He's incredibly sociable with both Cat Lady and me, and has adapted to the human household very quickly.
We had assumed that Pepper would strongly assert his usual alpha-male position, but instead, he's been quite blasé. Tiger, and to a lesser extent, Molly, have been the most aggressive in their posture towards Alpo, with growling and bared teeth. After a day or so of settling in, Alpo has now been doing the exact same toward Pepper and Lady, both of whom sure seem like they'd be willing to accept him if he would just calm down. Pepper looks downright confused when this happens, especially given that he's many times Alpo's size and strength. In no case has there been any actual physical confrontation, (yet), but it's been an interesting development in the previously-stable cat social structure here.
While it wasn't exactly intentional, the name "Alpo" continues the household pattern of two-syllable cat (and human) names with an accent on the first. :-)