Many of the Kubota owners here on TBN - welcome, by the way - get a copy of the Kub factory service manual for their series of tractor. The one I have covers pretty much everything from top to bottom. An amateur like me who can turn a few wrenches now and then will find how to fix most things, and a pro will find all the information needed to do a complete engine or gearbox rebuild. There is also a companion illustrated parts listing with all the part numbers for each model.
If you have to buy these items, they can cost a few bucks... well actually you'll probably lay out upwards of $100, but if you are buying a new tractor, maybe you can get the dealer to throw them into the deal at a discount or even free.
I don't know of any other shop manuals published for Kubota, but maybe someone else will chime in.