Transfer open invoice from one

I have 3 project organization say A,B,C and now we want to merge all 3 in a new project organization say NEWABC.We have open invoices that had interfaced through projects module.we want to move open invoices of organization A, B,C to new organization NEWABC . But we dont want to loose transaction number.

Please help me is there any way to migrate open invoices to new orgnaization without loosing Transaction number.