I'm afraid I must disagree with you, B.O.B. Castellano was NOT an Underboss. There is a lot of truth in what you say about Paul and Mr. Neil running different areas of the business, but they practically split into factions when Paul was named as Boss, skipping over Dellacroce, not before. Many people loyal to Neil, especially John Gotti, were highly upset that he didn't succeed Don Carlo, as he was rightfully in line to do so, as THE Underboss. This created a fault line under the foundations of the Gambino family. Neil magnanimously accepted Don Carlo's decision, however resentments in his faction built against Paul. Paul's greed, his hypocrisy and his self-imposed isolation from the rank-and-file added fuel to this fire. He was so ill-loved that only a few capos cared when he was assassinated.