One way or another you will "need" to remove the old fuel injection harness out of the harness in the engine compartment. There is dozens of company's out there like painless that can provide you with a new ot modified harness for the 5.3. When you get one, it will be up to you how factory like you want it to be. Want the motor to run separate of everything else? Then yea, get one of the "3 wire hook up" units and go from there. To make it look/function like factory, it will take some time and research like I have done to find out what all needs done to meet your personal goal. Some folks don't care how it works and looks as long as it runs right, and some folks want it to seem like they never did the swap in the first place. So your end desires are what will tell you what direction to go especially as far as the wiring is concerned.