If you have an LMG 5.3 you should be looking for an L96 6.0 or an L94 6.2.
L96 - iron block, 50# injectors, FF ready but no AFM with VVT. Oh and comes with 823 rec port heads , same casting as LS3 but different valves.
L94 - aluminum block (roughly 150# lighter), 54# injectors, FF ready, BUT...