Year difference in motor blocks

[Josh521]

I have a 2003 silverado with the 4.8l. Im needing a new motor figured a 5.3 would be easier to find and a better motor. But my question is what other year blocks can i use. Ive heard you can swap the 4.8 for the 5.3 with a tune. But could i fit an 04 - 06 block while keeping all accessories and fuel rails etc. I read in 04 it went to returnless fuel rails.