A good break-in procedure can help extend the life of an engine. However, even the best break-in will not guarantee long life since how the engine is treated afterwards is just as important.

I've used [link=http://rbmods.net/enginetempering.php]THIS[/link] method for the last 4 mills, and it has helped. I'm no metallurgist, but I still understand some the physics in what is described there, and I believe its the best way.

Also, I've never heard of an engine that ran 'well' at temperatures over 300 F unless it had an air leak. Most engines run best at around 230-250. Sometimes the ambient conditions will dictate temps even higher. But if you experience temps over 300 without a lean bog, I'd bet you have an air leak.