Just going by the pump I had whose model number equated to the combine pump, then I looked up the sizes for the pump gears on the Eaton site, they still make a similar pump with the same gears. Just from what I was seeing it looked like the longer gear was for the steering and the shorter gear, on the two stage, was for the pick up head. Without a bunch of digging I don't remember what the out put was but I bet you have some technical data I don't have. I agree, if its 7 gpm or greater it will work. I want to say the tractor pump was little over 9 gpm.
The two stage pump that was supposed to be the right thing had one pretty long gear and one little short gear. I figured the short one was for the pick up head.I still have the old parts if we need to do some comparisons. The shafts and gears are bad but the housing blocks are in pretty good shape. The shafts are no longer available from Eaton but the gears are. I had considered having new shafts made at a machine shop but found a pump for $50 and didn't thinks I could get shafts made for that.