I too enjoy the KIS look of my rifles.
I just built up a franken AR: Bushmaster 24" NM Hbar (Pre-Ban/No-Ban with A2 hider), RRA A4 upper, Ameetec Lower, and RRA parts/components with a cheapy BSA 8-32x44 scope that handled the recoil from 800 rd through a 7.62x39 Vepr.
It shot very high at 100yd (almost 12") and once zero'd at 25yd, it would hit whatever I was aiming at either in off-hand, prone, or in a bench position w/ XM193.
I still need to wait until my CC is paid off before getting a rear sight (either a detachable carry handle or a detachable rear sight, nothing fancy).
I have the standard A2 handguards and A2 buttstock like your 20" - I just love the stock/issued-style furniture!!!
I never had a problem with the hole between the pistol grip and trigger guard so "The Gapper" wasn't needed. My RRA Upper and Ameetec Lower fit so well that the only "play" I could find was a slight side-to-side motion that you'd feel only when shaking the rifle laterally, so I didn't feel an Accu-Wedge was needed.