V8 RPO codes? These codes are the V8 GEN3 style block.
L33 - Yes its a 5.3L engine with no Displacement on Demand, and it is a all aluminum engine. The block is a GEN3 casting, the heads are interchangeable from 98-06. This engine can be purchased very reasonable compared to taking a supercharged 3800 and adding the TOG's, Stage 2 intercooler, 72mm throttle body, and Multi Pulley System.
LM7 and L59 - Iron block GEN3 based concept engines. Not as much HP and torque as L33, and a little heavier.
LQ4 and LQ9 - 6.0L of iron block power. The LQ4 is 300HP, the LQ9 is 345HP.