John, 
 What I do know is that the tractor has a 504 minneapolis-moline engine, no turbo. The oil filter is in the oil pan accessable through an access hole in the right side of the pan. I have new oil filters. Time has been at a premium here lately so I have not had a chance to really get into the tractor yet. The brakes are shot, so i have to replace all that and wheel cylinders too. I haven't looked at the brake master cylinder yet, but the guy I got the tractor from told me he put hydraulic fluid instead of break fluid in the master..... death to the seals!
The exhaust manifold gaskets have a lot of blow-by, so I have to replace these too. (I have new ones)
   I have been dealing with Maibach equip. for parts and they have been super.
The machine had been through a tornado, so glass is cracked,lights are missing and the doors got wrecked, otherwise it is Ok.
 Something I will have to look at further..... If it sits for a few days, it starts hard, the previous owner told me that the fuel lines lose their prime, i.e., the fuel drains back to the tank. Well, to me that would mean that there would have to be an air leak to break somewhere in the fuel line, but all is dry, no leaks when the tractor is running. Once it starts, it runs well. The fuel tank sits lower than the engine and there is an electric fuel pump in line to get the fuel up to engine.
   I see engine oil on and around the rear of the engine, seemingly coming from the joint between clutch and engine.....I suspect a rear seal. I hate the thought having to replace that!
     What oils do the 2255's or the 1955's use in their differentials? would the 2655 also use the same? Would that also hold true for the transmission?
Most all the work will be pretty straight forward, but I would rather not guess at what oils I should be putting in transmission, differentials, hydraulic system, and drop box.
thanks for all your help. I really do apreciate it.
                                   Cal