Thanks Skyler and Dave. I should check the front bearings as I found a part missing in the rear wheel. I’ll pull it all apart when the spring arrives. I should add that the shoes aren’t contacting this drum but on a wheel that was on the bike previously.
Just to close out this thread, I installed the correct spring, chamfered the leading edges of the shoes more and roughed up the shoes again. I don’t know which, if not all of these things helped, but the squealing is much diminished. Not eliminated, but hardly noticeable. I should probably replace the metallic shoes next time around. Thanks to everyone for help and advice.