Get this wiring kit and you will have the 7 pin and 4 pin. No need for an adapter. I have a 7 to 4 pin adapter for my Z71 and it is just another thing to worry about.
https://www.etrailer.com/Wiring/Curt/C57674.html
I would cut the 4pin connectors off and splice all the wires together as opposed just to the plugging the new Curt 4 pin to factory 4 pin.
I know you are short on time but would be nice if someone with the factory 7 pin would show the harness behind the wheel to see if one could just buy the factory 7 pin harness and plug it in there. Since the Aux power is a fused hot wire they may have terminated it there for safety reasons.
Why they did not just terminate the trailer brake wire there too I have no clue. Also does not explain why they did not run the reverse light along with the trailer brake wire too.