No, sort_multiblock_read_count is just a new name for sort_read_fac. So that is the parameter to consider on instances running Oracle8 or earlier. However, the asynchronous read-ahead was only introduced recently so the merge width calculation details can differ accordingly. If you try event 10032, you'll be able to see how it is being done.

Prior to Oracle 8i, doesn't the db_multiblock_read_count have the same effect on sorts as the sort_multiblock_read_count in 8i which you mention in your most recent newsletter?