Forgive me if thesequestions have been asked already:

If one were to put a thumbhole stock on a post ban AR lower receiver, one could legally put an upper on it with a flash hider (no bayo lug), since the two allowable nasty features would then be the flash hider and the detachable mag, correct?  

Does anyone know if there is a maker of thumbhole stocks for the AR?

Its legal to own a upper with flash hider and bayo lug AND a post ban AR-15, just as long as you don't put the two together, correct?

No, a thumbhole stock is still considered to be a pistol grip under the 94 AW ban.  It only exempts you from having a pistol grip under the 1989 import ban.

This is because the 89 import ban and 94 AW  ban define the pistol grip differently.

Thanks guys.  Yea, I've seen that in photos also VA-gunnut, which is why I wondered about it.    

I've been told by an FFL dealer who has a large collection of ARs that the unattached lowers and uppers must be tagged, such as "pre-ban upper, do not attach to post ban lower", and that the pre ban and post ban items may not be stored in the same safe or "near" each other.