These are all very insightful comments and opinions. I'm glad to see a group that doesn't just unfairly hate on the two Joe's.
As for some of the ideas presented - I agree that neither Lou Costello or the Bowery Boys would have really worked. Besides being "bigger" than the Stooges (by that point, anyway), I think Costello was also trying to get away from being labeled as just a comic. And of course, as stated, he had health problems.
Leo Gorcey was in retirement at the time (though he eventually made a comeback of sorts). Plus, he was more of a Moe type.
Incidentally, Huntz Hall wasn't just a fan of Shemp's - they were actually good friends. The two met at Universal back in the late '30s/early '40s, and Shemp became one of Huntz's biggest comedies mentors. Shemp and Huntz later lived just around the corner from each other, and Huntz and his pal Gabe Dell would regularly attend gatherings at the Howard home. Shemp even became Gary Hall (Hunt's son)'s godfather.
Still, I don't think it would have worked out. Besides still being under contract to Allied Artists - and being "too tall," there was also a sizeable age gap between Huntz and the Stooges. Plus, based on stories I've heard about Huntz, he probably would have wanted all of the laughs for himself!
I know about the Mantan Moreland story (whether or not it's accurate is for another topic). He certainly would have made an interesting - though controversial - fit.
Hey, what about Emil Sitka?