I have a 3pt hitch log splitter, a NH 474 haybine, a KuhnGF 5001 THA Gyrotedder, a Ford 530 baler, and a NH 310 baller with kicker.  I don't know wether the cylinders are single or double acting.  My two tractors are a MF 1080 with two pairs of two hose hydraulic controls, and a Ford 1720 with one, two hose hydraulic controls.  Except for the Kuhn tedder all of the equipment uses two hoses, the kuhn uses only one.  I don't know wether these systems are closed centered or open, or how to tell, I just use them.

I don't own this Oliver 550 yet so I don't own any manuals for one either.  The Oliver 550 that I am looking at is more than 75 miles away so I don't have any way to take and post pictures but at this point I can say there is no lever under the right side of the seat, that is where we were searching for one.

What I would like to find out is what hydraulics the Oliver 550 has internally, for example to run the 3 pt lift, and did Oliver make a factory kit that may be available to equip a Oliver 550 to provide a two hose remote set-up, with a control lever.  My other tractors have a lever that allows the flow to be reversed so the piston can be extended and then retracted.