Thanks for that Kevin.
I'd found that one as well!
And things have moved on since I posted my cry for help.
Have asked the Bristol Parts gent over here to see if he has one in stock and he's checking - failing that I've found an outfit that will rebuild/refurbish what I've got if necessary -
SP Water Pumps - Car engine water pumps for all makes and models
So I'm hopefully sorted but would still like to know the definitive answer!
Having entered a variety of car runs all over the country am keen to get the thing back on the road asap!