Not as many , clutch fan posts, in the Ford Chassis forums as in the Workhorse forums.
But before you try body and grill modifications, it's important to check for a clean radiator, properly operating thermostat, and clutch fan operation.
In one of these posts, there is a comment that when engine temp reaches 209, degrees the fan should go to full lock up with the noticeable increase in noise , and the feel in the throttle.
The engine cooling fan takes 20>25 HP. to operate at full lock up, that's why the clutch fan is there, to limit that HP drain on the engine to the times when it is absolutely necessary for max engine cooling.
Found these posts in the Ford Chassis forums.
Clutch fan noise
Fan Clutch Whine?
Hope that some of the info is useful to you.