Rahul,
Products are not assigned to Work Centers. Or Resources.
Work Center Hierarchies are not transferred with standard CIF. You create Resource hierarchies in APO. See the appropriate help.sap.com doc under 'Creating a resource hierarchy'.
I suggest you tell the client you will transfer everything via standard core interface. Then, if necessary, you will make the appropriate changes in APO, either via CIF enhancement, or by direct editing.
You won't know what the details are until you actually have his system to work on.
Best Regards,
DB49