The only legal way to make a post ban AR pistol with the 10 1/2" barrel configuration is to perminantly fix the magazine in the well, thus eliminating it from being defined as a "semiauto assault weapon" because it can no longer accept a detachable mag. Keep in mind that that magazine must be fixed in such a way that IT CAN NEVER COME OUT BY NORMAL MEANS otherwise the BATF will still think of it as detachable. With the mag fixed and the weapon now legally not a SAW you can have all the evils except a stock, bayo lug, flash hider, wieght over 50 oz., you name it.
As for the pistol lower versus rifle lower thing, I think somewhere along the line someone needs to log the lower as a pistol. Once the lower has been sold as a rifle it cannot become a pistol so converting after purchase as a rifle is just plain out I think. As for a "virgin" factory lower, getting a manufacturer to log a lower as a pistol and then sell it to you might be a little hard. There is a guy here in the Saint Louis area that makes AR lowers and someone once told me he'd cast you a lower and log it as a post-ban pistol if you ordered it but as I have never done that I don't know if that is true.
P.S. I own two HESSE kevlar lowers. They both have Bushy guts and uppers and run just fine. Most of the issues with HESSE come from their total lack of quality control on all their parts but the stipped lower, which results in really shitty rifles. I've read on here about someone who burned up their kevlar lower somehow but I think that might have been a fluke.