In all honesty (and this will sound arrogant, and wel... it is...) Ext. Hist. is one of the easiest subjects out there.
Once the damned MW is done (39/40, oh yeah! - 3rd) all you need to know is half-a-dozen historians and historical movements (best ones being Herodotus, Thucydides, Marxist History, Postmodernism, Bede, and von Ranke).
And, as for the case study, well Tacitus is easy because it overlaps with the Ancient topics I'm doing.
So, my point is that this exam will not be hard. Oh, and it's on the 3rd last day - you have SO MUCH TIME to prepare, so don't panis... yet...