If you are good at drilling in tight spaces, give it a go.
But if you're like the rest of us not overly competent, give the Bing Agency a call, they have a range of services to remove broken parts from threaded holes in the carb body.
http://www.bingcarburetors.com/They will quote you a price for the service.
If you do get just one carburetor, be mindful, that there are a lot of different carbs in the 64 series carburetors, there is a vertical flange at the front of the carb, and it has a series of numbers stamped into it like : 64/32/325, make sure you get a carb with the same numbers.
The last digit in the series denotes whether it is a left carb or a right carb, an odd number is a left carb, and an even number is a right carb.
I clicked on the link that I provided, and it came up as a bad gateway, I don't know if this is temporary or not, do a search for Bing Agency International, and it will get you there.