When they designed the MGA in the 50s, I doubt that they took much time considering operating temperatures at the peak of Australian or American summers.  I am sure that the original MG-recommended position of the oil cooler works well in mild English summers or Aussie winters, however it is not recommended for hotter climates.  Many years ago, I discussed this cooling problem with several old timers who used to race MGs and Morris Minis for many years around Australian tracks.  They had all made some changes to their MGAs and other Morries, (some of which I discussed in Kermit's restoration pages).  This is another of their recommendations.

Assuming of course that all other pertinent issues are addressed (such as correct valve timing, correct carb mixtures, correct ignition timing, operating thermostat, good radiator condition, correct radiator cap length, brakes not binding, clutch not slipping, air not by-passing radiator etc) then repositioning of the oil cooler to one side of the engine coolant radiator and installing a radiator fan shroud (which causes air to be dragged through all of the radiator core rather than just the circular area in front of the fan) can reduce the operating temperature by as much as 15 dF (highway cruise in summer).   My experience experimenting with their modification over the years has proved their claims to be correct.  The move removes air flow restriction on the engine coolant radiator and reduces the "dutch oven" effect of the oil cooler being too close to the radiator.  The old guys definitely knew what they were talking about and their experiments worked well.

It's 5am on day two of having Chilli home with us and I am itching to get going with the work.  A check of the timing found that it needed to be advanced 10 degrees.  The front carb had a sticking piston, so I centred it's jet and then fine tuned the mixtures and balanced them.   Next came the repositioning of the oil cooler.  See pictures below.