This is excellent stuff, a very solid reconstruction. But I confess that I'm puzzled by your puzzlement!
If, as you suggest, you bottom out in the incoherence of the "vat-claim" after your reconstruction, what are you puzzled by? Nozick's idea is that "I'm not in the tank" is just like "snargleddeee snurglefooze bafoing". I don't know it, or believe it in a mistaken way: it's just that it never gets to count as something I might either know or fail to know. It just looks that way, but actually isn't.
Not sure if this helps: if you'd like to get together, I'm free Thurs afternoon at 4:00 or else anytime Friday before 1:00. Let me know if you'd like to meet,