Hi John, 
  Good to hear from you,You are a busy person! I see you are called on often on the Yesterdays Tractor web page.
   Well, I have an original and a reprint owners manual and neither gives specifics on any lubricants.  I also have the repair manuals and it says nothing either.  The capacities are listed, but when it comes to oils such as hydraulic, it only lists 10P3740. This is equivalent to a part number given for a 5 gallon pail of hydraulic fluid.
    For maintaining the drop box, it says   "Refill the main drop box through thedipstick opening with approximately 2-1/2 u.s. gallons of specified fluid."
  No where in the book can I find what the specified fluid is!
I may end up using something like John Deeres' HY-TRAN and I am only assuming here that this will be OK.  I recall we used to use John Deere TORQ-GUARD for dozer hydraulics.
    I may also look in one of my Kubota manuals as I know they gave quite a cross reference for oils. I just would feel better knowing that I have the correct oil.
  I suspect it has been a VERY long time (if ever)since any oils have been changed....the guy I purchased the 2655 from said he never changed the engine oil filter as it was in such an inconvenient location...he had the machine 10 years! YIKES!
  Well, if you come across anything, I would sure be glad to hear about it.
                       thanks,
                             Cal