I don't know how hard the spindle is. I'm guessing better then Rc55 (probably near 60). I have a Rockwell hardness tester (and heat treat furnace).
That and a boring bar to support the 5 inch cantilever cutting force is pretty big. The length of the spindle taper is a little over 4.5 inches. The deepest cut would be slightly over .002 (a skim to correct for the .0045 runout fit of the sleeve), which I don't know how good the surface finish would be after this.
From past experience using carbides, steel of Rc35 and more, I found to be a limit where the tooling was not destroyed. That has been my experience. I'm not using the most expensive inserts, and I really hate it when I have a $60 insert and it's instantly destroyed very few lathe tools have expensive (e.g. Iscar) inserts for that reason). Most of my insert tooling is on the mill, and I use brazed carbide mostly on the lathe.
This just seems to be a task that should use the tool post grinder. At least it will take several attempts to destroy it, where only one pass with a carbide can achieve the result.
I know I can find these grinding wheels. I need to solve the problem either way, assuming I ever need to do internal grinding work.