Has anyone tried deleting the hydraulic cooling fan in their M/Q 45, and replacing it with an electric fan?

Don't know about M's specifically, but SPAL makes some new brushless PWM fans that move more air than any engine could ever want. SPAL is very helpful if you contact them. The main issue you'll run into is fitting the shroud to the radiator. For a controller there are two I know about, Lingenfelter makes one p/n VSFM-002 and this one on eBay:

https://www.ebay.com/itm/143561612623

I've used the eBay controller on two projects, one for a customer and one for a shopmate. It's very cute and very simple, taps into the existing ECT and learns the temperature curve with button-pushes.