All spot on dave. yes it's not a A series engine with water shut off to matrix but you need to know that you are getting coolant flow adequately through the heater matrix and with the heater control to max you can feel thermostat open and closed at the matrix. Interesting point, I asked ford for a header tank and they said .... not available however Land Rover Td5 disco's have it fitted and they are available there but funnily not through Morgan. Liked your pipe link for cleaning and next time I will definitely be visiting boots for the tabs!
\have to say you're not alone having fun with that bloooody cap... my god I thought I was on the generation game!... nearly threw it!
