New guy here. Been doing tons of research and have decided to swap a 6.0/4l80e combo into my 1997 gmc 1500 4x4. Its got the factory 350/4l60e right now. I've got some questions though.

I plan to keep my original ecm to continue to run everything but the engine and trans. Keep gauges lights signals cruise etc. Running off old ecm. Then I want to use the donor trucks ecm for solely running the engine. I'm maybe a bit comfused as far as wiring goes. Is this what a stand alone harness is for?
I will be taking everything from the donor including wiring harness, ecm, exhaust manifolds, tranny, and possibly torque convertor. Everything attatched to the engine basically.
How should I go about this? By splicing the data wires the nbs ecm needs to run the engine from the old ecm? Or this is where say Nelsons stand alone harness comes in?