I know that there is a lot of compatible 4.8 and 5.3 internals that will fit, but I'm checking for a specific set and I searched and didn't find anything useful to answer my question. Will L33 gen 4 internals (rods and pistons), fit into a gen 3 LQ4 block from 2003

 

LQ4 is a 6.0L block with a bigger bore than the L33 which is a 5.3L. So no, they won't fit.