I used a "Cooling Components" combo shroud / electric "puller" fan on my '31 Ford (deuce shell and a Walker Radiator).
I bolted the fan / shroud up to the radiator and left a minimal amount of clearance between the water pump pulley and the electric fan motor, an inch is plenty. I am running a 350 Chevy, the water pump pulley is very low and nearly clears the bottom of the fan motor.
If you haven't bought your radiator, shroud and fan yet you would be better off doing so now. It will save you a lot of headaches mocking everything up now.