Incorrect installation by company maintenance personnel of the aft upper torque tube bell crank resulting in roll control that was opposite to that commanded in the cockpit. Contributing factors were the lack of maintenance documentation detailing the installation of the bell crank, the installing mechanic's incorrect assumption that the bell crank could only be installed in one position, and the failure of maintenance personnel and the flight crew to check the position of the control stick relative to the ailerons after the maintenance and during the preflight checks.