Van Nuys cars recieved the black under car paint. The Norwood cars recieved the red oxide primer. Several unrestored examples show this to be true. For example Jack Seymour's unrestored '70 Z. My old 27,000 original mile Cali '70 Camaro had black undercar paint. I'll dig up some photos for discussion.
Norwood '70 Z from NastZ28.com
Still looking for good undercar shots of my old Camaro...