I am in the middle of my L99 to LS3 conversion right now. Spending the extra time and money on the heads and valvetrain is the best thing you can do. Combining the right components will get you the best results in power and reliability.
For my engine I had Pat G. spec out a custom cam based on my needs and the intended use. I had my heads done at WCCH and am running all BTR valvetrain. You can see my build here:
http://www.camaro5.com/forums/showthread.php?t=271232