What indeed Mike... I could;
- leave my original carb alone, but I can feel some play in the bore and the cap threads are worn
- Have it bored out and re-sleeved? If this works I get to keep the original carb
- Buy a new 276 from Amal - for the princely sum of £350
- Replace the 276 with a more modern model or make - but I like originality and the space available could cause cable problems
People have different views, (thanks all!) so I'm a bit confused, but I'll see what Martin Bratby says in his reply, though I hear he's very busy!