Technician reported discovering a tail rotor gearbox that was installed on an aircraft was misrigged and assembled with incorrect parts that were not correctly documented.

Narrative

On Date I replaced a tail rotor gearbox with another unit that was freshly overhauled. Nothing on the [FAA Form] 8130 of the unit being installed indicated that it would have anything installed that the one being removed did not given that they shared the same configuration part number identification. Simultaneously; the tail rotor hub and blade assembly was replaced for scheduled reasons which had a slightly different configuration from the one being removed in that the overhauled unit being installed had the OEM trunnion bearing versus the aftermarket elastomeric bearing that the removed unit had installed. Following installation of the gearbox and tail rotor hub and blade assembly a minor adjustment was made to the pitch change link below the gearbox to correct for rig which is relatively common following the above maintenance. An operational check flight was performed and the Pilot reported no abnormal behaviors.On Date 1 a Pilot reported that he felt that excessive left pedal was required to maintain straight cruise flight. At that time we inspected the tail rotor control system verified rigging. An adjustment was made to the control tube located immediately behind the hat bin of the aircraft. Another operational check flight was conducted and no abnormal behaviors of aircraft reported by the Pilot.On Date 2 a Pilot reported that during his pre-flight inspection of the aircraft that he felt that the right pedal was not getting full travel as compared to other similar aircraft. At that time it was decided to do a complete rig of the aircraft. After performing the rig it was noted that when right pedal was applied that the pitch change mechanism on the tail rotor gearbox was at max travel before the right tail rotor pedal stop was contacted resulting in the limited travel that the Pilot was reporting. After detailed inspection of the aircraft including measuring the various control tubes in the system to confirm that the correct ones were installed it was decided to replace the installed gearbox with a different freshly overhauled unit. Upon arrival of that unit a physical comparison between the two gearboxes were performed at it was noted that the pitch change mechanism levers were of 2 different lengths. This was reported to the Bell Technical Representative who was assisting in the troubleshooting of the issue and upon research into Bell drawings it was noted that the links installed on the gearbox in question were believed to belong to a pitch change mechanism that is specific to the High Altitude Tail Rotor system which this specific aircraft did not have. The new tail rotor gearbox was installed; the aircraft was rigged; full travel of the pedals and contact of both left and right stops was confirmed; and a subsequent operational check flight performed with no further defects noted.Some contributing factors leading to the delay in finding and resolution of the issue:1. In the rig procedure in the maintenance manual; it does not state to confirm that the pedal stop is contacted in both full left and full right positions. It merely states to confirm clearances at both stops which is slightly confusing. The need to contact both stops is not clearly addressed in the maintenance instructions for the rigging procedure.2. Bell does not publish information directly regarding the different lengths of these specific links as they do with control tubes. These links are also painted and have no visible part numbers once they have been painted making it difficult to ascertain what units are installed after maintenance by an outside entity.