"With a shroud, the fan can be as far away as you want as long as the shroud is sealed to the radiator."
X2
The radiator should also be sealed to the bulkhead, and the entire bulkhead closed off from the grill except for the radiator face - all air reaching the grill must pass through the radiator. Old inner tube makes a good gasket for this.
One of the worst is sealing the nose of the hood to the top of the bulkhead, since otherwise air will just pass over the radiator into the engine bay. I've used air conditioning foam strips, but they have to be replaced every 2 years or so.
