Update: Car is back together fully again! Found out that the over filling of oil was not fully to blame for the lack of power, or at least I believe it wasn't. One of the turbo pipes had split... massively. Had to order one in from Ford and collect it on Saturday.
After it all went back together I gave it a check for leaks, there was nothing at all. Good stuff!
Put in the anti-freeze and made sure the oil was at the right level it should be and then took the car out to test! Started up perfectly, no strange noises or anything from the engine (Always a bonus), noticed immediately that the power it used to have was back, the car wasn't sluggish at all. Gave it a test for about an hour or so.
Once I got the car back home I let it stand for a while so that it could cool down. Few hours later I went to check the situation. No pressure in the expansion tank, water level was still okay, oil looked good still (not mayonnaise-like). Just gotta see how it goes!