A harvesting machine includes a harvesting header with a header frame, a flexible cutterbar assembly attached to the header frame along the length thereof and configured to cut a crop, a plurality of laterally spaced apart support arms, and a conveyor assembly positioned behind the cutterbar assembly and operable to receive severed crop material from the cutterbar assembly. The support arms are pivotally coupled to the frame for swinging movement about a laterally extending axis so that the flexible cutterbar assembly is operable to flex along the length thereof in response to changes in terrain as the header is advanced. The cutterbar drive includes a forward gearbox drivingly connected to the cutterbar assembly and supported on an outer support arm.
