@gmm67857 Well this has been years since doing this, and I didn’t write anything down or take pictures. I also don’t have this anymore, as I replaced my rack iMac with a Mac mini in a diy Ubiquity rack case.
But I didn’t have to disable or spoof any sensors to get the iMac project working. I just turned it on without the display connected, connected a mini DisplayPort to HDMI cable to an external display, and it worked. This was since replaced with a small miniDP emulator from eBay, to make screen sharing better.
I just took all boards out, and added low profile threaded mounting points in the bottom of a 1U case. Mounted everything as it was mounted in the iMac chassis, except the display of course.
I cut the power button cable, and extended it to a momentary button with a blue light. The light in the button did require 5vdc, so I just found somewhere on the logic board near the button connector that had 5vdc when the power was on, and soldered a wire from there and dc ground. Button would glow blue when the computer was on, and was mounted in the front panel of the 1U case, which was vented with lots of small holes. The bottom plate was also vented, as were the back.
I installed short adapters for the rear in/outputs (USB etc.) that had panel mount female ends, and those were installed in holes cut in the rear plate, along with an AC panel mount female connector.
I just used mine with Ethernet and Bluetooth only, but you can transfer the WiFi antenna to the 1U case and attach them the same way in the 1U case with hot glue. If you get a steel case, you’ll cut down a little on WiFi range. One solution could be using a plastic or aluminum case.