Well, this will get a few "different" replies - but being a 40+ year old tractor and the fluid that came in it from the factory was a Kubota UDT - you might want to use the newer UDT, S-UDT2, but being this is a geared tractor - any good, and there is the magic word - "good" hydraulic fluid will be fine.
Engine oil I would suggest 15w-40 Rotella or if a lot of cold work the 5w-40 Rotella oil.