They also left out his time spent with Jilly and the Colombos in Brooklyn.

Although Jilly's character made a cameo in the barbershop scene, I think they should have spent more time with Donny's initial contact with the mob as an undercover, which was not with Lefty, but with Jilly and then Tony Mirra.

That's the problem with adapting true life stories to the big screen, there's never enough time.