Improved support structure for suspending transversely adjustable row units of a cotton harvester or other implement from a unit support frame. A pair of V-shaped rollers, carried by a track on opposite transverse sides of the center of gravity of the row unit, prevent fore-and-aft movement of the unit with respect to the support frame and prevent contact between the unit and the track to reduce the effort required to laterally move the units. The shaft supporting one of the rollers includes wrench flats for receiving a wrench to provide mechanical advantage for easy rolling of the units, even in the uphill direction if the machine is parked on an unlevel area. The track support includes an apertured portion which receives a tapered, spring-biased pin which automatically aligns with the holes to firmly lock the row unit in position and to prevent the unit from accidentally rolling too far if the track happens to be inclined downwardly in the direction of desired movement.