I've done this too (no pictures yet, sorry).

I used a Mausberry use-your-own switch and followed this: https://retropie.org.uk/forum/topic/4011/mausberry-shutdown-circuit-nes-build-help

That enabled me to use the original NES power and reset switch, and the LED. Was pretty easy. Really the only hard part was desoldering the LED to flip it around.