Make it a woody too! A Dissapator/Woody would be nice.
Model1 sells Dissy barrels. Lots of options there. Traditionally the barrels were carbine gas, but Mod1 sells 16" mid length dissy barrels.
If you want to use an actual rifle length gas, I suggest making it into a piston gun. Otherwise you'll be stuck using heavyweight projo's all the time.
If you decide to build from scratch, and you don't buy a Dissy barrel, you have to get creative. I built a 14.5" 300Blk and made it into a Dissy. I suggest the YHM side clamp lo-pro gas block. Then the Armalite clamp on A2 sight.
If you like the A2, and you think you'll ever mount s scope, check out the flip-up A2.
I have a two Colt A2 uppers, a 16" HBAR and a 20" HBAR. I plan on a woody/Dissy for at least one of them.