The datsun 1500 / 620 ute(the model before the 720) diff is a perfect fit into the back of a 1200 with minor alterations.Its physicaly bigger (big axles big gears big evreything.) The length is spot on, the spring plates(the ones factory welded to the housing) are exactly spaced to fit the 1200 leaf springs. I know a fella who has already done his & the conversion looks quite simple.
It seems to be more than strong enough , He's running a1200 ute with a twin turbo rotry ,3.6:1 gears and 15" wheels producing abuot 350 +hp at the rear wheels(its awsome!!!) and the 1500 diff's still hanging in there.
Mod's to be done;
* Restud the axles & drums to suit (1500 utes use 6 stud rims). Check drums fit inside rims(may not fit inside 13" rims).Maybe a disc conversion is possiable??? ,who knows.

* Change tailshaft rear flange coupling to suit.(and maybe shorten) ???
Use the 1500 ute U bolts and spring/shock plates.

* SOMETHING TO THINK ABOUT NEXT TIME YOU HAVE NOTHONG TO DO ....HEY?*