About 50 years ago, I purchased a 1957 Ford Country Sedan.  I was going to pull the running 312 out and scrap it.  Life got in the way, and I decided to restore it.  It had the recirculating heater in it, but I would prefer the Fresh Air unit. Please let me know if anyone has one for sale.  I expect this to be at least a 3 year project. 

What is the physical difference between the two types of heaters? How does one spot one from the other? Was the "Fresh Air" a factory option, or a dealer installed option?

The dealer installed heater looks like a black box under the dash on the passenger side with an exposed heater core and a silver band across the front. It is very visible and looks like a Ford older design for cars and trucks. The upper block plate on the cowl under the hood is retained.

The factory installed fresh air heater pulls in air from the cowl plenum and blows it through an enclosed heater core and the air is discharged through a plenum that is more or less centrally located under the dash and it is less visible.

I have both and I could provide pictures if you need them

Update!  I do not need the dash controls or switch, but I need the outer dash trim for the controls.  Thanks!

Factory (fresh air) heater components.