I congratulate you on the Spal. Spal and Tri-Pac are the only two electric fans that work, and they publish fan curves. I have run an electric fan close enough to the water pump to run flat-head screws in the past. The engine movement is primarily side-to-side and not much movement fore/aft, so if you have 1/2", I would use up about 3/8" of it.

You could also run a pair of 12" pushers


The problems we face today can not be addressed at the same level of intelligence we were at when we created them - Albert Einstein Or with the same level of $ - Me