Yeah pretty much both the LS1 & LT1 have underhood computers (PCMs). The whole wiring harness can come out with the engine and that is usually how places like Hawks sell engine, harness, PCM, tranny combos
You will have to do some splicing like where the stock harness would plug into the vehicle body harness to power things like the fuel pump via a fuel pump relay.
Painless as well as a few other smaller companies offer LT1 & LS1 harnesses brand new with complete instructions and every wire marked. However these come at a premium because you have to do no research, just read and hook up. Any other questions let me know