I've been told that a Nissan Bluebird Series II diff center will fit into a Datsun 1200 ute diff housing. The 1200 ute diff housing is larger than the sedan or coupe diff housing, and thus the Bluebird center will only fit into the ute diff housing (thanx Chris Shoesmith and Ben).

David tells me that it's the Bluebird H165B (8 bolt) centre that will fit into a 1200 ute diff housing. He also says that the early model H165A alloy centre will bolt in, but the axle splines are a different size, and won't fit.