64 Dart 273 Engine Vacuum

Hi Guys, I am starting back for the winter to find out the problems with my friends 1964 273 Dart Convertible with a 4-speed.
How do I tell from any engine #s what engine we have? Not sure and it has been worked on many years ago. Is there any way to tell if it's originally a 64 or 65 273 w/ 2bbl or a 65 273 Commando 4-bbl.
Bob