I would be reluctant to try and straighten it by applying force to the other side. The metal in your frame was only .100 whenit was new and has most likely lost a bit over the years. If you are inclined to attempt to straighten the frame I would drop the pan so you can see just where the bend is. If you have a means of chaining the frame down either side of the bend you could jack up at the bend point.
However if the frame bent it is most likely time to slide some new material in the frame. This is a common method of supporting the older frames.
WBCCI 12156 AIR 3144 WACHUNG TAC NJ6
2004 Excursion 4x4
1991 34 ft. Excella +220,000 miles, new laminated flooring, new upholstery, new 3200 lbs axles