Einsteim,
Sorry about the late response, but I was out running the tractor all day. Must take advantage of the great October weather before the cold rains start.
Here are some pictures what I think is pretty much the same setup your friend has. The adjustable thingy (let's call it limiter mechanism) is swung all the way down and pinned in the lowest, out of the way position. There is a lonely hole near the bottom of the steel plate that serves this purpose. In one of the pictures I fashioned an ugly arrow pointing to the pin in the plate. The many holes next to each other are for the deck height adjustment, only used when mowing. I didn't have the deck on the machine and it supposed to be set this way as for not to be in the way of the 3ph operation. You can see the large cylindrical knob right under the lift arm just to the right of the ugly arrow. The lift arm actually rests on that when the mowing deck is in use and the limiter mechanism is pinned up in one of the several holes. That way you can raise the deck but can't lower it any farther than the preset height.
I hope this helps.
Best regards
Easygo