Both. Mafia culture in Chicago isn't like Mafia culture anywhere else. Whereas out east, it all sort of lumps & blends together. Chicago is something completely unique, from the accents, to the vocabulary, the street uniforms, everything. It would all have to be completely unique to this city, and to be honest, couldn't resemble any of the shows you mentioned if it were to be legit.

I agree with the late 70s though. Specifically the Chinatown Crew under the LaPietra Bros, that would be completely ideal. It'd have to be filmed largely in the Armour Square/Bridgeport neighborhoods as well, and who knows if that would even be possible.