Quick update.

B screw, and moving the wheel further back in the dropouts, got me to the ~5mm gap, tooth to tooth, between cog and sprocket that I read was recommended. Went through the derailleur adjustment procedure again.

It definitely seemed better on today's 17.5 mile ride. But today was with kids (14, 12 & 10), slow and flatter. I'll need a more aggressive ride to tell if it's good enough.

Pads were definitely an improvement. Installing the Kool stop shoes was a challenge, as the brake arms hadn't really had the slot finished over its whole length. It needed a little file work before the barrel could move up and down to adjust shoe position.

And, as I was putting the bike away, I realized that I think the left and right shoes are wrong! The part that sticks out to toe-in is towards the front of the bike, not facing the direction that the wheel will be coming from. Any idea if that matters, other than cosmetically?