Thanks for the advice. So, you think that if the breather was at one end of the valve cover and the PCV was at the other end that it would pull enough air that the crankcase would get some circulation too? Here's some pictures of my Mercruiser valve cover. Just click though them.
https://picasaweb.google.com/sodell3/292Mine?authkey=Gv1sRgCPXkrf2Zmp3lbw#5687557299774007362
It already has an oil fill and PCV hole. I could add a breather hole towards the back but don't know if it would be far enough away. Or I was thinking of buying a PES valve cover and having the holes cut at each end.
http://12bolt.com/250292_products/valve_cover
Steve