Seems like you have blown a piston. This results in excessive crankcase pressure (hence oil blowing out of breathers) and the burning of large quantities of oil.
Another possibility is a badly blown head gasket where combustion pressure is blowing into an oilway, though I think this is less likely.
A compression test may give you a clue.
You don't say if overheating happened first, if it did I would go with the piston/rings theory. At any rate, looks like you will have lift the head as a first step, then all may be revealled!
Mr. Toad
July 2008