Hi Bob and Jean
I don't think merging AP and AR datasets is the answer here. I think you just have to make sure the AP and AR control accounts are different in the two companies, and that the control accounts both exist in the master Ledger (usually I would suggest the same account, different department). Then simply retrieve both into the same Ledger.
Or is there more to this? For example, do you want to print a single aging?
Steve