I Don't Care. Do you?
You have to consider when something happens and be able to list out all the variables to find the solution. Stuff rarely just happens. It's usually the result of something you did. So ask yourself what has recently changed prior to the new "overheating" issue. From my seat all I can do is make observations on what you tell us. From your posts it seemed to me that the temp has been issue since the install of the EFI. This is why I suggest looking at the AFR and timing. Both of those have likely changed since the EFI install. The shop you use is used to modern stuff (high end even super type cars at that based on what you have shown us) where all that is computer controlled automatically. The mechanics are likely not well versed in old Ford tech. That 60's cooling system itself was often challenged just in normal "life". You've added air conditioning and a climate it never saw coming in some regards. Your auto trans also uses the same radiator to keep cool which means it also adds to cooling woes when things get hot.