I heard Ally Boy retained the title of Acting Boss when he went away and the guys actually doing the job have the Street Boss rank.
Do you remember where you heard or read that?
My understanding is, acting boss and street boss are basically the same thing. An acting boss is a guy who is on the street and able to run things day-to-day. In this case, because Carmine - the official boss - is in prison. Once Allie Boy went to prison, he's not really in a position to do that anymore and the title would be meaningless; not to mention inapplicable.
That said, I wouldn't be surprised if he gets the official boss title once his pop dies.