Well, I finally put the bike back together (mostly) today, and started it up. I put a whole can of Seafoam and 4 gallons of gas in the tank. The beast lives!!! Revs ok all the way through the range. No apparent leaks from the new water pump either. So it doesn't look like a carb cleaning is needed. But now that it's running again, I'm thinking of actually selling it. I'm lusting for a Triumph Scrambler and if I get a good offer on the Concours I'll have just enough to buy my first new bike.
Thanks for your help, everybody!