It is just a gear box so I don't think it is that big of a deal. I would thread the plug in to measure .@BXAK
Unfortunately an educated opinion is no more than a coin toss.
I would likely contact your local Kubota service department and see what they say, but that may not be the correct answer.
How about draining and measuring the existing fluid and comparing to the spec capacity? You don't always get the spec capacity back in when doing a fluid change, but refilling with the spec amount should put you in the ballpark.