Southern Cross Media will have its third chair in six months since taking over one of Australia’s most well-known media companies, Seven West Media this year after Heith Mackay-Cruise announced his intention to resign on Monday morning. The newly merged company, which includes Triple M, the Seven Network and The West Australian, appointed Rohan Lund as its chief executive in April, marking both significant board and executive turnover in a matter of months. Southern Cross Media chair Heith Mackay-Cruise is stepping down. Alex Ellinghausen Teresa Dyson, who joined Southern Cross’ board this year after eight years on Seven West’s board, has been appointed chair-elect. Kerry Stokes stood down from Southern Cross’ board in February, but his family maintains a 20 per cent stake in the company, and his son, Ryan Stokes remains on its board.…