Addendum. New idler kit came last night from FastLane, and I installed it. Of note, the included mounting bracket did not fit the engine - one hole did not line up quite right. Rather than try to bend it, I reused the filthy but functional old one. Although everythig else seemed to bolt in fine and the adjuster did its job, I could not get the indicator to work. It basically just did not move as I increased the tension.
Only a 16-mi drive to work so far, but none of the annoying noises I have been hearing for the past months. You can hear a little 4-cyl 'drone' under load, but muted, and overall a very quiet car.