Your patience is admirable, Flaminius!
As far as I know, generalised
am isn't used in today's African-American Vernacular English: see
African-American Vernacular English - Wikipedia. But I'm far from being an expert.
As to whether it was used in the past, you might be interested in this paper by John McWhorter:
Freedom Am Won: A Linguistic Mystery.
Overgeneralized am sounds so gratingly unnatural to a modern ear that even experts on Black English have long assumed that this usage was created by white minstrels.
[...]
But a great deal of evidence suggests that black Americans actually did use am in this way. The minstrels vastly exaggerated it, even as they savagely distorted black speech overall. [...] Historical am usage also demonstrates something counterintuitive, given the racial conflict so deeply embedded in this nation’s history: a great many of the roots of Black English reach back to the speech of rural white folk in the British Isles.