gibbons

I have a 2007 classic reg cab short bed with a 4.3. I wana switch it out with a 5.3 or 6.0. But i dont no wat all will have to be changed. I keep getting different answers about everything. Can someone please help out. Also what would be better. I just want a straight forward no bull answer. Im from Phx AZ but currently in Colorado springs Fort Carson. INFANTRY HOOAH