A disc mower conditioner utilizing a modular disc cutterbar to sever standing crop material by impact action supports the cutterbar from the header of the mower conditioner by a pair of transversely spaced support arms mounted by spherical bushings to the header to allow flexing of the support arms as induced by the cutterbar. The mounting of the spherical bushings utilize conical washers engagable with conical sockets in spacers to limit vertical movement of the spacer relative to the header when the corresponding support arm flexes. The mower conditioner header further includes an optional viney crop guide that has a curved leading edge that directs viney crop downwardly into engagement with the adjacent disc cutter. The viney crop guide is also bent inwardly to contain and control the flow of crop material. The mower conditioner swathboard includes a position control mechanism that incorporates a positive down stop in the form of a pin riding within a corresponding slotted opening in an associated bracket to prevent the swathboard from coming into an inadvertent engagement with the conditioning rolls.