If your on ramps or a jack you might find it easier to take the whole front of the car off, it comes off in 10 mins and does make it a lot easier so slip the box on, if your under a pit its ok to leave it on, its up to you.
Support the engine well, be prepared for a bit of a fiddle getting the box on, the diff tends to get in the way a little bit, you might be lucky and find it slips on lovly or you might not, Either way follow diamond hell's advice basicly, Other than being a bit of a fiddle sometimes its pretty straight foward! Good luck
