where are you agr012?

In Aus, 120Ys were both fully imported and locally assembled. The fully imported ones (mainly coupes) had a tiny little jap diff with a lift out centre, that's probably identical to the 1200 diff.

Locally assembled models had a much larger Aussie made Borg Warner rear loader diff and are all 3.9 ratio as far as I know. They have a tin tag on the rear cover with the ratio (3.89). Same width as 1200.

These same diffs were used in alot of other locally assembled jap cars in the 70's. If you are after a different ratio, KE25/30 Corolla's use the same diff, and have 4.1 or 4.3 ratios available in autos, manuals had a 3.89. Centres will not swap into the 120Y housing without alot of messing around, but the complete diff (drum to drum) will bolt in to a 1200. The diff is about 2.5 - 3" wider drum to drum, but will fit on the 1200 leaves without mods. Fit the 120Y flange and use the Y tailshaft. You will probably have to pump the gaurds especially on a sedan(depending on wheel offset and tyre size) or get fwd offset wheels. If you have Stanza (or similar) front brakes, it pretty well restores the front to rear track ratio. They also have much larger drums than the 120Y, but the same size (actually the same part No) wheel cylinders. The 1200 brake line will fit, just stretch the bends out a little to get the extra width. Handbrake would be a little more involved, I don't have the handbrake connected, as it's just a competition car.

I have used these diffs with a fairly strong L18, and have only broken 1 centre and 1 axle in 5 years - and only when using lockers.