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?

No fan will help if the coolant is not circulating at idle. Chris Ames's WP spacer addresses that. I have his spacer, but don't intend to use it until my engine is rebuilt. Chris is a nice guy and will talk your ear off, if you give him a call.
The smaller pulley would be the easiest repair, so I will wait until I know if it's needed. 

Not a Thunderbird but all my over heating in traffic was GONE with a 302 Mustang water pump pulley. All was bought from Summit, chrome was ruffed up and painted black. A spacer kit was also bought to help with belt alignment.

At idle there was no movement of water evident looking in the radiator. With the new pulley there was sufficient movement to keep creeping up temperature. I give all credit to greenbird on this site for tell me to do this 5 years ago. I do have the 1/8” hole in the plug I put in the bypass line 3 years earlier.

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

SOUNDS like you have most of the answers to water flow,1 exception is restricting the bypass flow you will promote cavitation especially in arias with no need for antifreeze. as the therm opens and closes the bypass eliminates cavitation. you won't notice until the therm aria will be eroded, as well the back cylendrs 4 and 8 will de eroded.  have used several blocks that when bored water was found required sleeves in those 2 cylinders,as water flows
around and up to cylinder heads. the better water flow you have addressed will increase cavitation as stat opens  and closes