Phil, something interesting:
A friend has very reasently bought a Morris 8 !
It's from 1947 and it has an 8 liter side valve engine which used to work with 6Volts but the previous owner made it a 12v vehicle.
Whats very interesting about this, is that this engine does NOT have a water pump ! It only has a large radiator, and circulation of the water is done by physics ! hot water goes up, cold water goes down, fan cools down whatever is in the radiator.
This friend has been looking for an electric water pump to fit on this car, as it overheats way too easily.
He found out that there is such a pump on the Audi TT's, to circulate the water that cools the intercooler
However, he is not sure that this electric pump will stand against the higher temps of the engine's water.
I'll be doing some research to see if I can find something for him.
Maybe you could consider adding an electric one to your system as well ?