There's a few vids on you-tube specifically about how to remove staked in uni joints and how to fit a new 'replaceable' uni joint. It's not that hard (though I must confess I haven't personally done it specifically on a datsun tailshaft. But as mentioned in this thread, the challenge isn't necessarily 'how to' get the old ones out, it's more a case of sourcing the right uni joints to put in to replace em with.