Have you thought about contacting Burlen Services, Shaftesbury as they manufacture SU carbs, stock spares and will rebuild if required.
This is a link to their
website ...
They are in Salisbury, UK and before becoming owners of the SU, AMAL and other British Carburetors were a Morgan dealer!
The owner, John Burnett, has retired but the owners son has taken over and he is a total petrol head!
New SUs are now made using modern materials and CNC machining, they are alcohol in fuel proof and polished look fantastic. Chromed dashpots are available...
Contact them for advice, but in general once the body of an old carb is worn to the point that the butterfly spindle needs bushing other internal parts and passageways will be worn and the thing needs replacing, not repairing.
