This article is not written to convince the reader of the virtues aluminum radiators. Other articles should have done so already and if you are reading this you  have been convinced. As simply put as possible, aluminum radiators dissipate heat more efficiently than traditional copper-brass radiators for two primary reasons:

1) Copper-brass radiators must be soldered together. Solder is a very poor thermal conductor and inhibits the ability of the fins to pull heat out of the tubes. (Although aluminum does not dissipate heat as well as copper-brass).

2) Modern aluminum radiator designs incorporate wider tubes with smaller cross sections. This design allows for more contact area per cubic inch of coolant, and allows the radiator to cool substantially better than older designs using narrow tubes with larger cross sections.

3) Aluminum is much much (2) lighter and capable of enduring the constant flexing of the traditional Morgans. 

4.) The newer Morgans, fit with a plastic radiator, have reported an ever growing rash of cooling issues (overheating) especially when the bhp climbs over 200.  More horsepower means more heat and they fit the same rad to 4/4s (100 bhp) that they fit to Roadster 3.7s (280 bhp). Sad. My recommendation is to swap them out for something better on arrival. 

If you restrict you purchasing to the USA, there is a better option than Griffin. one with a great reputation, going by the name of Ron Davis Racing Products. RDR knows Morgan rads better than any in the USA and has done many. The joints on the rad are welded very very well. I found the cooling ability of my Ron Davis rad better than my Griffin (tests back-to-back on the same day, roads and ambient temperatures). They can also flush mount a high powered SPAL fan if you so choose and I very much recommend that for the pre-2000 cars that can fit one.  Much of the cooling issues are caused by inadequate fans used prior to that date.

See the RDR Rad to the left and right. Note the thicknesses!

Their service is very good. Expect to save 10-20% on a Griffin package after everything is factored in. They also weld the joints rather than epoxy them.... MUCH better than Griffin (see the Griffin comments who has been known to use epoxy in those key places. They too will not use a plug-in Otter switch but they can offer you a range of rad fan switches or make the threaded fitting you wish. (Big engines see the BMWs above). Most US dealers use them..likely a knee-jerk reaction for a home-grown product.  BUT, bless their hearts, if you wish, they can order from Mulfab as easily as you can.  

Two important codicils. 

1. The RDRs for made for the bigger-engined Morgans are unwisely designed. And these are most often the Morgans that need better cooling the most. The Roadsters, aside from the very early ones already fit with aluminum rads at the Factory, come with inadequate cooling directly from Malvern..much as the Plus 8s did. If driven as they should be (why buy a sports car and drive it as tamely as possible?) they boil over with stock cooling. You CAN get adequate cooling from the MMC (they use Mulfab as well) but only if you ask for a "performance upgrade" at the cost of the Mulfab. RDR (I was there when they did it) decided to address that by installing a thicker core. I had the first of these. They have had success with that with other cars.  But trad Morgans have always had a problem with airflow through the rad..as it is canted at 30 degrees. The thickness of the core determines the resistance the radiator the allow airflow through it. The best race preparers in England have correctly noted to me (they have the results from professional airflow chambers) that this forces much of the air around and over the radiator..not helping in the cooling process at all. There are methods to address this (which I will explain in another article when I find the time) but the punchline is that RDR's super thick core for bigger engined Morgans, combined with Morgan dynamics creates a very poor result as well as making installation of both the rad and a better fan super difficult.  I doubt RDR or the Morgan dealers selling them are aware of this, but there you have it. Mulfab increases the cooling by making their rads thinner..allowing more airflow THROUGH the rad and adding more capacity by lengthening the rad at the bottom (not really visible) You can also obtain them through Morgan Spares (aka Morgans of New England).

Using my original Morgan Plus 8 (copper) rad as a starting point, my big Morgan engine was 5C degrees cooler under normal driving conditions and 9C cooler under stress conditions with the Griffin. The time it takes to cool from 108C (fan on temperature) to 88C (thermostat closure) was approximately 7 minutes at 60 mph. However, the Ron Davis Racing rad was 2C cooler than the Griffin under all conditions (tested on the same day, same car, same coolant on the same road). BUT the Mulberry beat the RDR by an additional 3 degrees in all conditions and cooled from 108 to 88 faster. To this one must add the effect of the better SPAL rad fan when NOT moving.