Have you tried, or you should try-when you get back to working on this great looking car- Going back to a mechanical fan, with a shroud, and also with a clutch. Make sure all gaps are sealed around the radiator so all air getting into the engine compartment needs to go through the radiator. Plug any unused holes in the radiator support.
You've replaced a few freeze plugs. Have you given the engine a good flushing out? Mine was loaded with scale and casting sand.
If you still have issues, it is a pro-touring car, put some hood vents on either side, about in line with the pulleys. Air moving up and over the car will draw more air through the radiator and out of the engine compartment.
