Checking in. I went to the Park Tool video and followed it. And tried every set of pads I could put my hands on. The only ones that showed any improvement are those same KoolStop. I agree they are not the best choice, but also I realize that I simply don't have access to vintage bike parts. The other model suggested is certainly the better option, but I can't lay hands on them. As I was getting ready to move on to something else, I remembered another stash of brake pads, including another set of KoolStops and a couple brand new KS inserts, and will fiddle with them this afternoon or, more likely, tomorrow morning.
I also have the option of drilling the brake bridge, in order to install the Tektro long reach sidepulls I have. But I have not yet made the decision to do that. This bike functioned perfectly in August of 2021, so it's just a matter of figuring out how it was set up then. Memory is a terrible thing to lose.
Edit: I have long been under the impression that the toe in was to be corrected in response to noise, and the Park Tool video , in part, confirmed that. Nonetheless, the adjustment has been made and it's working better. I have hope for the next round of pads.