Tom,
I remember it to be a cover over the Roof Hatch. The roof hatch would allow hot air to escape up and out. The problem was cinders would come down and in.
The K-36's (except 484, 485 and 488) got something similar in function but different in design about the same time frame you are asking about. The K-36 (and K-37 for that matter) Vent covers were flat sheet metal with a approximate 45 degree slope down to the roof at the front and the back.
Kevin Cook