Cervi2015

Looking for some information, I bought a 2004 2500hd 6.0l and wanting to clean it up, new fluids, ignition stuff, shocks and a few others. I started looking into shocks and bilsteins which led me to trying to figure out if any modifications to the level of my truck has been done. its a 2wd and already sits fairly level, I haven't actually measured it but just looking it its not far off. The keys look to be untouched so I don't think they leveled it that way, one question I did have is the rear shackles. It has them, did they come stock with shackles??? Any other way besides jacking up the front with torsion bars or lowering with shackles that leveling can be done?