Abstract: A conversion unit for a pickup truck long-cab chassis frame, modified to support a regular cab, thereby providing a frame clear length of almost two feet between the cab rear wall and an open front end of the cargo bed. The conversion unit includes a plastic bedliner portion, defined by bottom and opposed side panels, and a self-supporting, integral, forward extension portion defined by an extended bottom panel portion, extended side panel portions, and a front panel upstanding from the forward end of the extended bottom panel portion. A metal framework, embedded in the plastic extension portion, is adapted to be secured to the frame clear length providing an extra-long composite cargo bed. A second embodiment of the unit provides a lower-half opening in one side of the extension portion, adapted for closure by a downwardly opening lower hatch swingably supported on the framework.