I agree with the earlier comment on doing a thorough cultural assessment – identify the similarities that you can highlight and build further. Also identify the differences and understand how tied each group is to those elements, are they open to change or are they at the core of their very being. Plan for it to be a long term game, you won’t be able to change the critical elements overnight. Also understand what has to change in Year 1 and what’s negotiable for the parent organization, building out a strategic plan with a logical flow will help to make smaller steps to close the larger gaps in culture. You’ll always have some differences, I’m sure you see them by office or business unit today in your own organization. Best of luck!