Hi again,
Reading the additional info, looks like you've done quite a bit already trying to improve the cooling system.
You might try adding "Water Wetter", made by Redline. Most find it drops temps 10-15 degrees. There is a new product for similar purposes, claiming even greater temperature reductions, but I don't know if it works, nor do I recall the name.
Recoring without a crank hole would be help the existing radiator quite a bit. The other posts makes good suggestions, too, about increasing the capacity of the radiator, although there's not a lot of room for a big increase.
The 6 blade plastic fan will likely help a lot.
Some folks don't like auxiliary electric fans in the "puller" location, i.e. in front of the radiator. The concern is that it's blocking air flow to some degree. I'm not so sure about that. Once you have the plastic 6 blade fan installed, you might experiment removing the electric fan for a test run, just to compare.
Also, there are various size and air volume electric fans. I've got a 14" puller just recently installed on my TR4 that's rated pretty high, but also pulls enough amps that I'm converting the car to use an alternator. It will likely be noisier, too. I've seen as large as 16" fans on TR radiators.
If you do end up shopping for a radiator, I still recommend aluminum if possible. Most of the repro radiators are long neck style, so will fit your car. Either Victoria British or Moss had one, I think, but I'm not sure if it was aluminum.
Other key factors, do you drive in hot conditions alot? Does the car have engine modifications, headers, anything that could make it run hotter and keep underhood temps high? I've just replaced the mild steel headers on my TR4 with stainless, one major reason was to be able to wrap the headers to reduce heat in the engine compartment. Mild steel can be ceramic coated, but I believe wrapped stainless gives the biggest temperature drop.
I hope you find some solutions.
Alan