Can I have two uppers for one pistol lower?

[Untamed1972]

What would the minimum upper need to be for the spare rifle lowers to keep one out of constructive possession (assuming that you cannot have spare rifle lowers and spare pistol uppers lying around).

In other words, if there is an issue with quantities, is the following kosher:

1 complete AR pistol
1 complete AR rifle
3 AR rifle lowers, each attached to a stripped upper
1 AR pistol upper

You just need to have a legal use for the short barreled uppers.

Cuz if you think about it, if you have a rifle and pistol you are already in posession of everything you need to construct an SBR in about a minute. But it's not constructive posession because you have a legal use for the SBupper, ie the pistol. So you have an extra SBupper, as long as you have a pistol you can use it on, you have a legal use for it. It's when you have a rifle and an SBupper and no pistol that you're in trouble.