I haven't forgotten. I have watched several flicks in the name of research:
Blackula
Coffy
Cleopatra Jones
Black Caesar
Black belt Jones
Caligula
In short, Black Caligula has mutated into The Decline and Fall of Black Caligula and the Badassssss Foxes from Detroit. I think this is mostly a change for the better, although Black Caligula, the character in my head, is now some sort of kung fu vampire. I'm not too worried about the logistics or historical accuracy since many of the real deal stories about Caligula are fake or exaggerated anyway, so I don't see any major issue with turning him into a black vampire. Elements of the Patty Hearst SLA story are also working them in, but before anyone gets confused, the character based off her is NOT one of the Badassssss Foxes from Detroit. The Badassssss Foxes from Detroit are, of course, an all black, all female gang that are partially inspired by the Lizzies from the Warriors, with added blackness and kung fu and lesbianism.
also Black Caligula is sometimes reminiscent of Boddicker from Robocop. I think Kurtwood Smith in blackface might be a wise casting choice, actually.