I have three build plates in front of me, all from B310 wagons.
One is a WHB310 & it came with a diff that was coded HA38. I think that the 'H' in WHB310 means the A14 engine as this is what it had while the HA38 is a H150 differential in 3.889 to 1 [3.9] ratio.

The other two plates are from WPB310's with HB37 diff codes. I think that the 'P' in this case is for the A15 that they both had & the diffs were H150b in 3.7 to 1 ratio

HA= H150
HB= H150b as best as I can tell.
Since the H150 series diff that you have is from the earlier 120Y & is in 3.9 to 1 ratio, I would guess it is an H150[a?]

Feral seemed to think that the H150b used a lower mounted pinion, which meant that the gear teeth would be at a different angle, but in the H145 & H165 the 'B' version of the diff meant a switch away from the fixed length sleve & shim method of pinion preload adjustment to the collapsible sleve method.
I do not know if this applies to the H150, but for diffs that take a fair floggin', I prefer the earlier method as there have been instances where the collapsible sleve has been known to collapse just a little bit more, resulting in a pinion that could move & ultimately, a noisy diff, with all the bad things that result from such things.

I think I need to talk to you about that differential, ..... soon.