I had a similar problem on a '64 Falcon. there was only 2 1/2" of clearance between the radiator and the water pump pulley. I found a 16" fan with an offset motor and belt drive called a "Sidewinder." They claim it moves 2200 CFM and is only 1 7/8" deep at the center. It's expensive, but it's well built, works good and solved the problem. Below is a link to where I bought it.

Link to Sidewinder