I had heating problems with my 40 216 car motor, at slow speeds. I found a nylon fan blade that fit a Datsun, with about 7 blades on it. The center hole was big enough to fit over the Chev water pump. It made a world of difference in slow speed temperature. Sorry I don't remember what model it came from. The 4 blade fans just don't pull enough air, even though they were all you had back when.
