Finally got Hellscream's Shield Wall on my warrior from a normal Garrosh kill. Post-patch, and making use of the 100% heirloom drop rate, I had killed him once on my warrior on heroic and the 1H dropped, but no shield. Also killed him twice on my paladin while loot-specced as prot and both times the 1H dropped instead of the shield. Finally killed him on my warrior on normal mode with no 100% heirloom drop rate and got the shield. Seems like the 100% heirloom drop only applies to weapons, not shields or offhands.