The 5.3 heads do have smaller combustion chambers but the valves are smaller

 

no they are not worth it...

 

some good info on most of the stock GM heads. no idea on the accuracy of any of the numbers.

http://www.smokemup.com/tech/ls1.php

 

Prob just stick with the stock ones for now. Had the motor out and the heads off. Also have some LS1 heads and 706 heads laying around. Probably going to send the 5.3 heads off and put bigger valves in them later on. Stock for now though.