Yes, when removed from the carrier, the bolt fits, into the extension fine. On the reverse of that, with the bolt removed, the carrier fits perfectly into the upper and slides into the gas key fine from what I can tell (ie, it goes completely into the upper and is flush with the rear of the upper.
I'm going to put a 5.56 round in the barrel to make sure it seats correctly and is the correct barrel and extension.
I was at a gun show yesterday and took the upper with me in the hopes of finding a bcg for sale that I could test fit into my upper, unfortunately I didn't come across any for sale. I highly doubt a gun shop would allow me to swap BCGs with one of their working rifles....I don't have a relationship with any of them around here.
I want to try another bolt in the carrier, and if that doesn't work, I suppose I'll have to find a gunsmith.