There are a number of after market suppliers for add on air conditioning units. They can supply all of the parts, brackets, pulleys, etc that are needed. If they do not include an auxiliary fan, buy one. Flatheads are notorious for barely adequate cooling systems for around town use. Also, have your cooling system thoroughly flushed, and maybe even have your radiator specially cleaned before you use it.
I have sent my radiator to Walker to use as a model. They are building a four core with transmission cooler and ac condenser. I have just returned from Lake Tahoe Early Ford V8 National Meet. I found a car from Mississippi and another from Georgia. They both had driven their air conditioned flathead cars cross country without overheating.