Side Note (which may or may not be of any use or interest): Both my BN2/100M and BJ8 behave exactly the same WRT running temps: They both have 180degF thermostats, but will run well below 180 on cool days on the highway, 180 on warm days on the highway--though the BJ8 will start to heat up pulling a long uphill grade, e.g. Hwy15 heading east to Vegas--and both will heat up sitting in traffic on even cool days. Both have fresh engines, both behaved the same before and after overhaul; the BJ8 has the stock baffling--but with a minimal fan shroud--and the 100M, of course, has a louvred bonnet. I've heard of engines that (always) run cool and Healeys, of course, can run hot but engines that run too cold sometimes and too hot at other times seem to defy the laws of thermodynamics.
Side Note 2: On a recent episode of 'For the Love of Cars' they restored a Triumph Stag. I didn't know much about the cars but, apparently, they were notorious for running way too hot, and subsequently ruining engines. The restorer, named 'Ant,' loathed the car at first but seemed to acquire grudging affection for it as the show progressed. The engine teardown was a bear as the engine had not run for a long time and the major components were 'fused' together. After a meticulous overhaul they brought the car to a guy who supposedly trains pro racer crew chiefs and put it on a rolling road. Ant expected the engine to overheat, but it ran perfectly on the dyno and the expert declared the engine temps were all nominal. The expert concluded that the engines built at the BL factory were being built under duress--BL was on the cusp of BK at the time, I believe--and hence were never assembled properly, but a properly built and spec'd engine was a decent V8. Ant had bought an aftermarket aluminium radiator with an electric pancake fan, but decided not to use it. My point: A properly built and sorted AH engine will perform adequately in any conditions the average car will ever see, and slapping an aluminium radiator 'band-aid' in the engine bay is not necessarily a panacea. As Keoke pointed out, copper and brass are better conductors of heat than Al, and the primary advantage of Al radiators is a bit of weight-saving.
Side Note 3: Ant also took the car to an 'expert on what engines sound best' (or something). He brought both a 12-cyl E-Type and a Kubota riding lawnmower for comparison to the Stag. Ant expected the Jag to blow away the Stag in the 'most pleasing engine sound' department, but the expert declared--according to his algorithms--that the Stag V8 had a better note than the Jag (but the Jag did 'beat' the lawnmower).
Side Note 4: One of the reasons--expense being primary, I suspect--that newer cars tend to have 'idiot lights' instead of honest gauges was that your typical driver--not gearheads--don't know how to interpret gauges. When my dad was a factory rep for Ford he said people would bring cars into the shop saying they were 'defective' because the oil pressure gauge showed a drop from cruising speed to idle. Same with the temp gauge; anyone else notice how modern cars' temp gauges always read nominal, no matter the environmental conditions and load? Not saying that's the case with Healey owners who, by necessity, tend to know more about cars and engines than your average Camry driver, but is it possible we're overly nervous about normal fluctuations in gauge readings? Case in point: if my temp gauge didn't show some heating sitting in traffic or pulling a long uphill grade on a hot day, I'd suspect the gauge, not the engine.
Moral of the Story: Make sure your AH engine is in 'proper nick,' as the Brits say, before trying (possible) gimmicks (I expected Jet-Hot coating the exhaust manifold to help my BJ8's heating issues, but I saw no quantifiable change--$400 wasted). My best explanation for otherwise well-tuned, overheating engines is crud buildup in the block and/or radiator; tend to these possibilities first.