yes Bumpy Johnson did exist, he along with Leroy Brown were instrumental in the Harlem "Mafia"... there is a book called The Enyclopedia of Gangsters or The Encylopedia of Murderers (i can't remember the exact title...it's been so long since i've read it, so don't quote me.) It has all these intersting details and stories on all of the famous and not so famous gangsters of the 20th Century.
The movie itself was lacking...Andy's performance along with Roth's was pretty good.
My favorite part of the movie...the food loving hitman brothers. I know i wasn't the only one who thought that was funny!