yeah... while I'm not sure if its in the manual or not, there are locks up under the tractor that allows you to lock the deck up when you want to just use the 3ph. I use them when I take the deck off for the winter to keep the arms from dropping down when I use the 3ph.
On each side, you'll see a piece of flat steel rounded with a hole on one end and a spring loaded pin through the other end. Pull on it and rotate it up... the hole will lock onto a fixed pin and hold the deck up. Just make sure you do both sides.