Hi I think you will find the Mini estate and van sender unit 21G2054 / Smiths part number TB1114-031W will fit and work correctly along with gasket 2H1082 and Screws ARG923.Check with The Riley motor club spares dept as they may have stock.
I bought the chrome wing strips from club spares in 2014. Not sure what the stock situation is now though. If you're a paid-up member of the Riley Motor Club then you should be able to see what is available.
Thank you very much for your help, highly appreciated. We have been in contact with Spares Responsible person. Looks like Spear is available, Fuel Tank Sender Unit unclear but probably can be purchased elsewhere if club doesn't have it. Yes, we are "paying member of the club". We are running " a club" ourselves, and a museum. www.oulunautomuseo.fi.