My source is "Critical Assembly: A Technical History of Los Alamos during the Oppenheimer Years, 1943-1945".

I thought that book had the full story on Jumbo, but it does end with 1945 so it isn't really complete.

They also built one-tenth scale Jumbinos for testing. The Jumbinos had holes blown out from the explosions and were left in a trash dump. They were rediscovered many years later by a jogger.