The parts catalog doesn't distinquish between tractor models when describing the hydraulic pump and manifold, so generally, they should be the same for the different models. Beginning at the front and rear and working towards the middle, the tractors are the same. The differences begin with parts having to do with the transmissions, such as engine flywheel and differential pinion shaft. Anything more than these general statements is beyond my knowledge.
801 is the Series number that describes tractors with "4-wheel adjustable front axle and 134 cu.in. gas/LP or 144 cu.in diesel engines." The middle number, such as 4, will be 1 through 8 to indicate the Model, and describes transmission, PTO and hydraulic options. 871 is SOS with single-speed PTO and 881 is SOS with 2-speed PTO. regards, George