A harvesting header (40) operable to harvest a crop. The header has a header frame, a flexible cutterbar assembly (48) mounted to the header frame to extend lengthwise in a lateral direction relative to the normal direction of travel of the header and which is operable to flex along its length in response to changes in terrain as the header is advanced; and a draper assembly supported on the header frame behind the cutterbar assembly to flex therewith. The draper assembly includes a pair of side drapers (52) and a fore-and-aft draper (54) located between the side drapers, the side drapers being configured to receive severed crop materials from the cutterbar assembly and convey the materials laterally to the fore-and-aft draper. The fore- and-aft draper is configured to move the severed crop rearwardly, and includes a draper frame swingably supported on the header frame at a pivot to project forwardly therefrom. The fore-and-aft draper includes a draper belt supported on the draper frame to present a rearwardly moving run for conveying the crop rearwardly, the draper frame having a forward margin which is coupled to the cutterbar assembly such that the draper frame is caused to swing relative to the header frame as the cutterbar assembly flexes up and down. The fore- and-aft draper also includes a counterbalance mechanism (210) coupled between the header and draper frames to counteract the weight of the fore-and-aft draper about the pivot so as to reduce the load of the fore-and-aft draper on the cutterbar assembly.