That dovetails nicely with my previous post mega.
You see the name 'Karosserie' at the bottom of the data sheet? It's 'Ihle' - BMW didn't build that body, Ihle did.
The first BMW with the twin-kidneys was model 303 in 1933. Pontiac was using a vertical separator on it's grilles in '31 (
http://www.pbase.com/xl1ken/image/58366006) possibly earlier.