Gully, I bought the spare carbs some time ago cheaply on ebay. They were not originally from a GT6 Mk3 but they were the same basic version as mine so I had them refurbed and rebuilt with the correct needle/jet/spring spec for my engine. I have another pair of new old stock GT6 Mk3 carbs but they are to Swedish/US spec with slight variations to the UK spec.
Nick.