I'm currently reading into the English version of Mafia Inc. which is about the Rizzuto clan.

The writers confirm that Arcadi was Rizzuto's street boss, or acting boss, when Rizzuto was sent to prison.

This is what is stated:

"After Vito's arrest, police had pegged Arcadi as a possible successor. He was the clan's street boss, liasing with Outlaw bikers and Montreal's street gangs. Reporting to him were two younger men, Lorenzo Giordano and his associate Francesco Del Balso".

The book states that Vito and Nick Rizzuto, Paolo Renda, Rocco Sollecito and Francesco Arcadi formed the upper hierarchy of the Rizzuto organization. If I remember correctly this is also stated in the Sixth Family.

The book also states that Morena Gallo was a high ranking member and that Tony Mucci was his lieutenant.