The brace is no longer relevant. They are saying that oops we made a mistake, these braced pistols should've never been allowed, and now your in possession of a prohibited SBR. And per the existing rules, a foreign made braced pistol (now SBR) is already assembled and thus cannot be brought in 922r compliance. So either surrender it to us or destroy it.
Now granted the doc is piss poorly written, but this is what it appears to be.
That is not correct.