Stabilizer bars are available both rigid and adjustable. Adjustable types are threaded, and function exactly like a 3-point hitch top link. The 'flexible' kit that Sam described are probably 'adjustable'. They're used to offset an implement. A pair of rigid bars for older Fords costs under $20 at Tractor Supply, and a pair of adjustable bars are about $45 (mounting brackets extra).
It's common to use only one bar instead of a pair. but to me, it doesn't seem right to place all the stress on one side. regards, George