That's what I believe also. He headed then or prior one of the NY families, but not the Corleones.
Which family do you think would that be then?
I personally think Altobello succeeded Pentangeli. He was way too close to the Corleones to be a rival mobster of another family. I think he was referred to as Don by Michael simply because he was the Corleones oldest friend and Connie's godfather.
Some months ago I made a topic of my thoughts about this:
http://www.gangsterbb.net/threads/ubbthreads.php?ubb=showflat&Number=604759 
