Converting Assets with Source Line Level Detail

I have never done this before, so I was curious about the gotchas.  Our client wants to converts assets with source line level detail.  In WebAdi I can include he invoice number, but these assets will have multiple lines that make up the total cost.  If we use a custom process and the additions api, not mass additions, we would have to populate the fa_invoices table to be able to view the source lines through the asset workbench correct??  Are there any rules that govern if the source lines apear in the asset workbench?  Once the source lines were in