If my memory serves me well a diff out of a datsun 1200 or 510 is a R160, the rear diff in subaru legacy rs & gt's (4.111 5spd 4.444 auto's)is a R160 also and I think they are interchangable.
http://locost7.info/files/differential/Datsun-Suba ruDiffInfo.doc
I'm sure one of those may help