Wilcox and Lang's "brigades" together contained no more than about 1,500 battle-weary men on July 3 and so I doubt they would have had much impact on the outcome even if they had been following right behind Kemper's brigade. So many Union reinforcements were rushed to the point of the attack from every direction, among them several 12th Corps units from Culp's Hill, the remnant of the 3rd Corps from south Cemetary Ridge, and numerous batteries, that I rather think another full-sized Confederate division would have been necessary to achieve a decisive breakthrough, but that's just an opinion. Tom