Work streams for a "slow" integration

I have a hard time understanding why it makes strategic sense to move that slowly. However, if the steps are small and slow, I would likely not focus on making it 2 separate teams out of it. Assuming the work in year one can be completed in year one, have the team that completes the year one work roll over into the full integration in year two under the guidance of a steering committee or oversight group as appropriate. Supplement the existing team with the additional resources required for the full integration giving you both continuity from year one to year two activities and the necessary resources to execute the work.