Dear,
A difficult task considering data inconsistency and a highlevel ERP minds need to be get involved from all functional and technical areas to achieve... As the financial year end is nearer try to convince your team to management to get this to be implemented from start of new financial year keeping old tranactions intact without any changes.
Anyway managemnet decision will be the final if they are ready to bear !!!!!!!!!
http://wiki.sdn.sap.com/wiki/pages/viewpage.action?pageId=58884811
Regards,
Syed Hussain.