Yes, certainly sticker shock with the prices - I've still got to find a roof and repaint the car (as well as a host of other stuff , some yet to be discovered I'm sure

)
Phil, your Google search abilities are better than mine, I found one place selling them
here but I've decided to risk getting a float and replacement gasket and hope it's a uniform size.
I also scraped the paint of the original sender and found the Smiths Serial number
TB 1114 / 028 in case that's of use to anyone.
As always, thank you to everyone for insights and help and my first Morgan meet up was hugely inspiring to keep at it !