I built my first 97 in 2005 installing an 02 LS6 and used my factory harness and added wires like Jeff said. I was able to make everything work including the gauges using is HP tuners and the 02 Ecm. If you don't like spending time reading schematics and tracing out wires from both vehicles do what Jeff said and talk to Allen and get you a harness. You can make that 5.3 scream if it's a regular cab and add a cam and 3200 stall in the transmission. You can find diagrams in the stickies but you'll nead the c-100 diagram for the 97 so you'll know which wires to remove from the 97 harness. It really sounds more complicated than it really is. Once you get the motor in then the fun starts.