Like the others said, 90 is not that hot. One of the big issues cooling 7 type cars is getting the air to go THROUGH the radiator rather than AROUND the radiator. An indicator of this problem is that you get higher temperatures at speed versus in traffic. Both of the Fraser's I have had have run hot in traffic but fine on the open road and at the track. If yours runs OK in traffic but not at speed then I think you have an air flow issue. How hot does it run when in traffic on a hot day? (quite hard to test with our weather at the moment!)
a) Check that the temperature gauge is correct
b) Make sure the system is bleed with no air locks, you might need to jack the front of the car up to get make sure the cap is clearly the highest point
c) Block the air gaps around the radiator to ensure air is forced through it
d) If you are using an electric fan is it run the right way for the side it is mounted on?
Electric fans are more efficient pulling rather than pushing air through the radiator, but again on 7's packaging is often and issue, on the Fraser it pushes.
Nice MG too.