The whole "Constructive Intent/Possession" thing is very murky, and you will get many opinions on it.
IMO, if you have a pistol SBR with one short upper, and a regular AR rifle with one or more uppers >16", then you are fine.
If you have multiple short uppers, you may be in a little more risky area. IMO you would still be legal, though.
If you had short uppers with no AR receiver that could legally use them, then IMO you are asking for trouble.