Hi Mik,
First thing - the best money you can ever spend on your Datsun whether you're are a mechanic or not is to purchase a workshop manual. Here is a link which should help you out (starting at $10 you can't go wrong)
Datsun W/Shop Manual For SaleRemoving a diff is really quite simple - if you haven't done it before then have a mate come and give you a hand.
Make sure you have got a decent jack and safety stands as well.
Things you gottta do
Tailshaft has to come out, rear wheels and brake drums have to come off, undo the brake pipe fitting on the diff and at the wheel cylinders, axles have to come out, leaf spring " U " bolts have to come off, depending on what you are doing with it - drain the diff as well.
Check there are no other mounting brackets on the diff connecting to anything that you are going to break if you leave them connected (like handbrake cable mounts, brake lines etc.
"Remember when you jack it up to jack it up off the chassis and SUPPORT THE REAR OF THE VEHICLE ON JACK STANDS (so the suspension is sagging down at full travel)"
Once you are at this stage have the trolley jack under the center of the diff while a mate keeps it balanced on the jack and then slide her out.
PS: Unless you are going to be removing the diff center itself you won't have to worry about removing the axles.
BUT GET THAT W/SHOP MANUAL FIRST AND IT WILL ALL BECOME THAT MUCH" CleAreR"