Hey mate, I did exactly this at Easter this year and it's a massive PITA to do, but a great learning exercise. If you haven't got it already, go and be the d22 PDF manual that you can download through a link here on the forum and surf through that for a bit, there's instructions in there to assist in the sump removal and replacement - namely the correct order and torque settings for the bolts.
Stick the front end up on chassis stands - VERY IMPORTANT. Never work under a car suspended only by a jack, and sine you're having to remove a cross member, it's better to be safe than sorry, plus, you will want every bit of extra room under there you can get.
Also borrow/beg/steal a trolley jack, it will make the job of removed and re-installation of the 50-ish Kg front diff assembly alot easier.
Your best bet is to do a forum search for the Lokka DIY write up that forum member 180%JOE did - he goes into great detail about how to safely remove the front diff.
And a pro-tip for removing the engine sump - remove the steering drag-link as well, the sump will just drop into your hands and you won't have to spend 2 hours trying to weave it out. Because at the front of the block is the drain or something, it makes it very difficult to get the sump out with the draglink where it is, I ended up needing to unbolt the idler arm and tying it as far out of me way as possible.
Also, chances are that the sump is currently being held on with some liquid gasket type product - it will prove VERY difficult to remove. I found that a Stanley blade works well for sliding in-between the sump and block to get it started, then ingot a small paint scraper in and worked it around the entire sump. Then you'll have to get a small screw driver in and lever it up as you work the blade around.This task alone took me over an hour.
To remove the old gasket off the sump, I used a wire brush and some good old fashioned elbow grease. Again this took a long while to do. That liquid gasket is TOUGH!
I'd definitely allow a full day to do this job properly, and make sure you have a mate to help.
Good luck!