Looks to be a stabilizer bar that would prevent the attachment from swaying side to side. Lift arms should still go up and down.
Some tractors did have additional "fixed" stay straps that would connect from lift arms to under top link the don't allow 3 point hitch from raising or lowing. Used for a "fixed" cross drawbar on the 3 point hitch.
The chains limit the adjustment, probably so the arms dont' get caught in the tires.
Going to be really tough to get bars into tires as the add on bars are actually rigid length and pushing inward...
Dale
You missed his point Dale. He meant the chains were there to keep the arms away from the tires. Which is mostly correct.
The add on stabilizers are much better at controlling 3pt sway.
Older tractors used chains and then pin on stabilizers that were usually non adjustable to control sway to a finer point.
Its matter of perspective.... Chains are ineffectual with bars in place, remove bars and chains are again valid....
Dale