Could be different from truck to truck but mine looks to be around 8 1/4 inches from back of core support to the threads on the water pump.
you can get some room by flipping radiator upper brackets from back of core support to the front.
Could also cut threaded snout off waterpump since you aren't using a mechanical fan.
lastly, you could offset the electric fan so the motor doesn't interfere with the pulley...
What electric fan are you using? Taurus, Volvo or something else?