Any progress?

Some.

I bypassed the heater matrix and that seems to have helped a little. I have a replacement water valve for the heater but haven't fitted it yet.

The car is now stored for the summer. Yes, I know that sounds wrong but I spend summer in Nova Scotia and leave the car here in Florida. I expect to have to do more when I get it out again in the autumn. It is a lot of hot iron in a tight space. I have no doubt more airflow through the engine compartment would be a big difference but don't see how to achieve it.

David