A bodies were. There was an obscure B body manual disc brake option in 1970 listed for B body taxi cabs. I have an NOS master cylinder listed as being for 72-74 E bodies with manual disc brakes, which may be for 72-74 B body also. I’ve never actually seen a 72-74 B or E body with manual disc brakes in person or in a magazine article, but seeing how those years usually get ignored over their 70 and 71 predecessors that doesn’t mean much.
