Hi all
With lack of finding a better alternative, I simply made a view which linked SalesLine and CustConfirmTrans, displaying SalesId, LineNum, and Min(CustConfirmTrans.RecId), and then made a query which linked this view to the CustConfirmTrans table proper by Min(RecId) = RecId.
Again, I'm sure there must be a more efficient way of doing this but I had a deadline :/