I had the same problem with a later 235 in my '50 COE. Contact Patrick's in Casa Grande, AZ. They have spacers the correct thickness for just this purpose. Unlike other vendors, they make and sell the spacer, along with their short shaft pump. As I recall, the spacer is less than 1/2 inch and the spacers you get at most auto parts places are 1/2 inch and larger increments. One half inch sets the fan too close to the radiator.
Kent

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1950 Chevy COE Model 5700 ~ "Barney" ~ And more pix