Failing a more reliable source for the Smiths petrol gauge tank unit, they
appear on both eBay sites(ebay.co.uk is the other).
The Rootes part number is 1223569 for Alpine III-V up to
B395009549 (GT) and B395009420 (sports tourer) and Tiger or Alpine V8 up to
B382002361. For later cars, the Rootes number is
1238848 and this number supercedes the earlier part number.
The only other number I have is a Smiths part number of
TFS9002/000 and it is said to cover Tiger/Alpine V8 production dates Oct. 1964
to May 1966.
If it doesn't come with your part, you should also get the sealing gasket
number 5040662) and if needed, the locking ring (Rootes number 5040663).
Obviously, it's one of those parts where LHD and RHD don't matter.