The last focus fanitic mag had an article on how to install the quaife. I don't think they split the case. I'll try to find the mag and let you know. I do not think that torsen makes a diff to fit the svt. The quaife to fit a focus is around $600, the one for the SVT is an additional $400. Just happens to be the next investment on my car.
Anaxagoras - I might do it at the same time as a new clutch/flywheel combo so it will be a fun little project if I decide to go through with it. I also heard that it is really hard. I also think that you do in fact need to split the case cause I think you are supposed to use a Ford tool to get it open
bobo - i am not sure but i think Torsen might be coming out with one soon if its not already out (cheaper than qualife)
The Quaife is better due to the torque bias ratio? Quaife was 4.5:1 and the Torsen was 2.5:1. Quaife will even warranty the part for use in Motorsports/racing, so no worries there, but Torsen?? who knows.