Di Carlo was allegedly a captain in the US Marines who was assisting in this re-establishment exercise, and would have obviously supported Dr. Navarra who was in fact his cousin. It would have been a short step from backing a mayor to backing a new boss of the other side of Corleone. There is, however, doubt that Di Carlo was even in Sicily, as he was deported back to Italy sometime after 1947.
Maybe it's a different Di Carlo? The biography of the one I talked about is presented here among other mafia biographies
http://legislature.camera.it/_dati/leg05/lavori/stampati/pdf/023_002223.pdf(sorry I found it only in Italian) and there is no mention of him ever leaving Sicily.