A fan is going to do very little to solve the problem… I can offer the following suggestions as I live in an area where the ambient temps in the summer are in the triple digits.
Alloy radiators are a waste of time… Brass radiators provide better heat transfer and are repairable. Alloy radiators cannot be repaired and are throw away parts..
I have had a new core installed in my factory radiator with “dimpled” tubes. This slows the water down and keeps it in the radiator longer, so it has a chance to actually cool. I have a standard (stock) water pump. High volume pumps will just make the problem worse. I have fitted a reduced diameter water pump pulley… You can get these online from ebay from the guy in Thailand…. This will provide a faster fan speed. I have fit the LAT type fan.
It’s also a good idea to fit the horn hole blanking plates. This keeps the hot air from just being recirculated through the radiator. The main problem with the Tiger is that there is no way for the hot air to get out of the engine bay.
There are several things that can make this much worse…. Headers are one source of excess heat. Timing too far advanced is another and the mixture set too lean is just another nail in the coffin.
Rootes recognized that there were cooling issues on the rally cars and ran them with the hood on the safety catch (partially open)..
Based on my own car I can make the following suggestions… fit the horn hole blanking plates, reduced diameter water pump pulley and LAT fan, re-core a standard radiator with a dimpled tube core and run a standard water pump and a 160 degree thermostat. Make sure that you have fit the factory fan shroud.
I have a 302 with a Holley 4bbl (vacuum secondaries). Set the timing at 10-12 BTDC and set the idle mixture screws to give a slightly rich idle. Lean mixtures and timing too far advanced will contribute to high coolant temps. Set the idle speed to 8-900 RPM
You might also consider an oil cooler. With the previously mentioned items my car would hold operating temps in the middle of the gauge, regardless of traffic or ambient outside temp.
I made a steel LAT hood and my operating temps are now well below the center of the gauge.. I have verified the operating temps with both a cany thermometer in the expansion tank and with a laser thermal gun….