The only RHD Subaru's i've ever seen are 1990's legacy's. So the simplest guess would be a 1990-1994 and 1995-1999 difference.
Only 1990's legacy rack difference Im aware of is the gear ratio, maybe that's the difference here - are the number of teeth/splines on the shafts that would change steering ratio different? Maybe the quicker rack has beefier gland or something to support quicker steering ratio?
CARDONE has a rebuild service listed on rockauto.com - for $218 you mail them your rack and they rebuild it and return it to you. This link may not work - but just drill down to your vehicle on rockauto.com and under rack and pinion is a rebuild option:
https://www.rockauto.com/en/catalog/subaru,1996,legacy,2.2l+h4,1269873,steering,rack+and+pinion,7388
I assume it would be unavailable if you ordered it but here's Subaru's RHD rack:
https://www.subarupartsdeal.com/parts/subaru-rack-assembly-gear-box~34116fa000.html
This place appears to have sold rebuilt ones before:
https://www.detroitaxle.com/shop/steering/rack-pinion/complete-power-steering-rack-pinion-assembly-right-hand-drive/?vyr=1996&vmk=Subaru&vmd=Legacy&vsmd=Postal