I love Datsuns and miss my old 720. Anyway you are in for alot of work. For crawling you're going to have to put in a solid axle. The tcase output is centered, so a new divorced tcase is in order. Although i have heard of 3 guys who added a second tcase after the stock one. If it was mine i'd add a yota dual case with an OTT divorced adapter. Or maybe a Dana 20 with a low gear set.
Next you need axles. They came with 4.10 but i think there's only 1 locker option for your rear, which is lockright. Find a matching set of Dana 44s from a waggy, or Dana 60s if you need them. The rear is extremely flexy! Hang the front with some yota or waggy leafs.
I'm guessing your datsun is worth up to 2000$ max if its in perfect shape. You'll be into this double that at least depending on how much you do yourself.
If i didn't already have too many projects, i'd love to have what you are contemplating.
Reality is though unless you love the Datsun name or look or something, you'd be better off to get something more common with straight axles already on it perhaps.