Secondary Ledger with data conversion method JOURNAL

Client needs to add a secondary ledger to an existing primary ledger.

A couple of questions: 

If I use Conversion Method  JOURNAL - the secondary ledger is populated with data by the GL Posting Program.

Do I still need to create / select a SLAM (subledger accounting method)? The modified SLAM we use for the primary ledgers is linked to this Chart of Account. So I don't think we can use it for our Secondary Ledger (which uses a different chart of account).

How do we populate the history with conc program: SLA Secondary/ALC Ledger Historic Upgrade - as that only works if the data conversion method is Subledger Accounting and if the same SLAM is used.