The issue of whether or not there were five families or six is probably THE most-often discussed topic on these boards. A current discussion is on in the "Godfather Novel" board.
One thing's certain: if there were a sixth New York family, it wasn't the Molinari's. Here's the transcript:
MICHAEL
Wait a minute -- you took Freddie in because the Corleone Family bankrolled your casino --
because the Molinari Family on the Coast guaranteed his safety. Now -- we're talking
Ntra la porta tua lu sangu � sparsu,
E nun me mporta si ce muoru accisu...
E s'iddu muoru e vaju mparadisu
Si nun ce truovo a ttia, mancu ce trasu.
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