I've got an old post ban (late 90's) A2 upper that's sat for many years. It's currently a cheap 16" HBAR, mid gas as it came from Model One Sales from Shotgun News ordering days... Any thoughts on what I could build off this upper? Would it be reasonable to expect a good barrel and good BCG to result in a good shooter? If so, I'd lean toward a 20" A2. Otherwise I'd likely go SBR short. Thanks.