"Midnight Charger" I remember too. A particular mix of equipment, usually. Not unlike the normal "Spring Special" models of old. I suspect the "Sport" in Monaco SS had to do with the vinyl bucket seat interior and the "Cordoba" wire wheel covers?
Seemingly, the "Midnight Charger" had to do with a "Magnum-type" grille, padded landau vinyl top, with specific opera window 1-divider ornamentation. Many pictures in Google Images.
They had to have SOMETHING to talk about as "power" certainly was not in those conversations, back then.
Just some thoughts,
CBODY67