Can't remember everything involved, but I do recall bending the battery tray upwards at the corner nearest the alternator with a large angled pliers. It'll bend easily enough, and bend back just as easily. This will give you a little more room to rotate the alternator and slide it out towards the rear. I didn't remove the power steering pipes when I did mine. It's a case of wiggle, rotate and tilt, but it will come out.
I know it sounds a bit dim, but I can't remember whether I took the inlet manifold off. I've just been out to look and I suspect I did remove it as doing so would allow a lot more room to access and manouver.
If Syd is your only means of getting to Great Yarmouth then I would be a little concerned of running out of time. Ok, I'm not the fastest spanner in the west and it was very much a learning curve when I did mine, but 3 hours won't give you much time if things don't go to plan.
I don't know what the problem is with your current alternator, but if it's not charging I'd stick the battery on charge tonight and drive it with minimum use of blowers, rear demister etc. for tomorrow. Once it's started, the battery isn't needed to keep the 2.5td running. You could actually take it off and it'll still run.
If overcharging is the issue, as it was with mine, I'd keep the revs below 1500rpm and drive with the lights, blowers etc on. I drove mine for over a week like this.