At least it's big enough so you can use a good-size boring tool. On the other hand, it's also big enough so you'll be needing to take a pretty hefty cut, which may chatter.
I've never done internal Acme threads, but obviously, you need an accurate tool shape to get the thread form.
Any chance of buying an Acme nut of the proper size and turning down the o.d. of that to make the insert? Finding one with 2.2" worth of thread might be a problem, but if you could get one, that would solve the thread-cutting.
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