After the loose spark plug fix, I found that the decompression valve was sticking open. This saw's previous owner was using it for some shovel logging, or something, and had a branch fall out of the tree and crack the top, inner dog bolt hole, and the decomp valve shaft was bent, so I never used it. Not a big deal to me either way on a 460 and smaller. Anyhoo, I was able to remove the valve from the outside, easily, as I think Brian indicated, squirted it with some penetrating oil, which I think was Al's advice, used vice grips and channel locks, and straightened the bent shaft. After working it back and forth some, replaced it, fired it right up.
The reminder diagnostic lesson I'm taking away from this is that if a saw strangely stalls periodically after running just fine, check the simple stuff, like is the spark plug wire on tight, or is it just close enough to arc, and is the spark plug tight, or just enough to have okay compression at high idle. The new lesson was, sometimes the decomp sticks open, and is easy enough to fix.
Thanks for the tips.