Wiring harness - Your stock 5.3/60e harness will work, I know a 60e to 80e adapter is out there. The 05 harness can work, but in my opinion it is not worth the trouble. You can also find an 02-00 6.0 4l80 harness to use.
ECM - You're stock ecm will work if you use an 02 or older wiring harness, although it will need to be flashed and retuned with the 6.0 parameters. I recommend going through Nelson Performance.
Fuel - You will either need to change the fuel rails on the 6.0 to a return style rail, like your 5.3 has, or run a WIX 33737 filter/regulator with the 05 returnless rails.
You will also need to change the oil pressure sending unit on the 6.0 if you are running an older harness. Here's the part number "acdelco D1818A"
Do some 4l60 to 4l80 google searches. There are plenty of articles out there on this subject that will explain it better than I can.
I may be missing something, but this swap is really straight forward. Hope this helps and good luck.
2000 RCSB
LQ9
Torquer V2
T56 Magnum
305 drag radials
3/4 lowering kit