New here guys thanks for reading and any advice or knowledge dropped is much appreciated first off.

I have a 03 silverado that originally was a v6. I swapped in a 5.3 lm7 that I rebuilt, my question is could I use the ecu and harness from the 04 silverado that I took the engine out of or should I source a harness for a 03 v8 model. I'm not sure what harness work and don't work. Also seen some harness on ebay and Amazon that says they will but just not sure. I'd like to be the easiest way since I'm not building a show truck. Plug and play best way and oem hopefully.

I also know that my Truck was dbc and the 04 harness I have is dbw. I do have the harness ecu and throttle pedal and tac module but read that they were more complications in the 03 models about the wiring. Not sure.

I'd just like to know if it would be good to just change the truck over to dbw since i have everything or just find a new harness that's dbc and stay cable and just change throttle body?

Thanks