The original diff in an Aussie Sunny sedan was an H150 in 3.9 to 1, however an H145 in 4.11 to 1 from a Datsun 1000 or early 1200 ute will fit & I guess that this is what you have.
The axle centerline in the H145 diff will be 2.5mm forward of the original & there is no easy way to remedy this, but you probably don't notice it with a welded diff as I presume it to be.

The next standard ratio up from the 4.11 to 1 would be the Sunny's original H150 in 3.9 to 1. This diff, ... in this ratio, was used in all imported Datsun 120Y's [Aussie built sedans used a Warner rear axle assembly] & all Sunny models except the very late, A15 powered Sportswagons which had an H150 in 3,7 to 1 ratio.

There was also an H145 in 4.375 to 1 used in Datsun 1000 Vans & Utes & a rare 4.625 that was an option in these two models.