https://www.vintagecarparts.co.uk/en/976~sparking+plug+adaptor-details/
I get mine from there, not worth making them myself for that price! Remeber to buy the washers too.
The problem with NOS is it is several decades old and you don’t know the storage and transport they get subjected to. Given they have been through factory closures, auctions, autojumbles et al NOS plugs are usually not a safe option from my past luck with them.
Interesting thread though.
Cheers,
Rich
