That's unlucky! and a very bad start.
It's exactly why I would always try everything in the book before doing a carb strip as it nearly always opens an unknown can of worms, but hey ho, you had no choice really.
I would try an easi-out on that sometimes called a stud extractor. You might have to drill the hole out a bit bigger perhaps to get one in, but they do go down to some very small sizes.
Get the carb body held carefully in a vice or get some thick gloves and then pour boiling water on the body when you're ready to apply the easi-out. You could also soak the body in penetrating fluid while the tools are coming in the post or whatever.
Good luck, you will start to move forwards with this soon I hope.
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