Do you have any possession of any pistol AR, or any stripped lower receivers? If so then you can have your 11" upper today.
Really it comes to intent and how hard the ATF wants to go after you. Likely they wouldn't unless you have other stuff going against you on some major bust. Don't take this as you can just go buy a spare autosear for your M16.. I'd wait until you have you M16 in hand.
There are a lot of gray areas which typically get interpreted different ways by different agents, etc.
Your HK examples.. without the sear, they are SBR/AOW so don't leave them in that configuration if you take out the sear.