The big takeaway from the RV pump comparison is the difference in flow at low rpm between the impeller designs. The first pump with the large 8-blade impeller seems to move the most coolant at idle or near idle. Since I apparently need to increase either or both coolant and air flow at low speed I will be using a remanned 8-blade iron pump with the large pulley, unless I find an 8-blade pump already on the engine, in which case I will swap to the smaller AC pulley. There is also a “compromise” Hemi pulley that falls around 120%.

If these changes do not work I will look deeper - radiator upgrade, internal blockage, etc. I had the car out for a while in November on a 50’ day and it stayed reasonably cool so I am optimistic that putting some things back to stock will get me where I have to go. The crank pulley is not stock so it could just be a drastically under driven 6-blade pump providing poor coolant flow combined with a lack of shroud and aftermarket fan causing poor air flow.