RVSM Requirements
One of the commonly overlooked procedures associated with RVSM operations is that your active transponder must get the altitude data from the same place as the autopilot altitude hold. If you have an autopilot that follows the altimetry system of whichever side is the PF, as some do, then you should make sure that you flip the transponder (or transponder source) accordingly.
Conversely, if your transponder can only receive data from the LH air data computer, then you must only couple the autopilot to the LH ADC when in RVSM airspace.