Quote:
Did you ever solve this mystery?

I tried to apply a little logic & just came up with more questions. Lets see what we have.
1. It's not an H165, so if it is a late 60's or 70's Datsun diff, it must be a H145 or H150.
2. It has the large flange of the H150
3. The 4.11 to 1 ratio was used in H145's but not H150's
4. It uses an iron carrier, so that rules out early H165's in P410 & P411 models along with H145's from B10 models.
5. You say it 'fits' Datsun, but did not say that it is actually a Datsun diff. Could it have come from something else?

So what have we got? It's smaller than the H165, it uses the pinion flange that suggests H150, but uses a ratio that was available in H145's but not H150's.

Any positive answers?

EDIT
I just noticed that the side bearing adjustment is done with threaded adjusting collars & I don't remember these being used in Hitachi/ Datsun diffs

Was it the borg warner that Toyota had in thier corollas that was the same time as 120y's? rules that out I guess