Ah - I see you've added a picture, which answers the rest of the puzzle.
The first Horning GMC 12 port head was used on a 274 cu. in. GMC and put into the remodeled Marvin Lee streamliner, "The City of Pasadena." The old Model of "The City," had run a 12 Port Wayne Chevy engine to record setting speeds. "The City of Pasadena," was first run with this new combination at Bonneville in 1951. With Puffy Puffer at the helm, the car made a couple of trial runs and then went for it. Well, it went too fast or something, because the car got sideways at over 200 mph, and flipped over. This accident fortunately left Puffy alright. The motor was saved also, but the car was total loss