[redmodelt]

I would use the one with the arm already on for a driver, but if you need to keep the correct arm for judging, just replacing the shaft would be the way to go. The carbs I have rebuilt were not for show cars, so was not an issue.
If the hole in the carb body is worn but not too bad, pretty sure you can get the assembly with oversized shaft or re-bush the hole as needed if you can.