Now that summer is on it's way, I am thinking about making additional improvements to my TBird's cooling system. I already have an aluminum radiator and electric fan.  Made a big difference.  There are a number of additional modification available. Casco sells a water pump with deeper fins.  I believe this is to compensate for the TBird spacer.  They also make a smaller water pump pully which is supposed to improve flow at idle.  I have also seen an improved spacer. My issue is only when sitting in traffic on a hot day.   As soon as I move, the temp returns to normal. Any input?

How much smaller is the Mustang wp pulley?

The stock one is over 7” the Mustang is right 6” outside diameter. I believe Ted said once there were different diameters for different parts of the country.
Some have had concerns about to many rpm on the pump and cavitation. I suppose this could be a problem if drive at 5000 rpm continually. Think about your alternator or generator and how small the pulley is. I had the stock 3.21 gears in for 4 years before changing rear ends to a 2.74.

56 Vic, B'Ville 200 MPH Club Member, So Cal.