Using an off-the-shelf Terminator head replica, I was able to create a Terminator themed PC for a client fairly quickly and easily.
To match the case to the Terminator skull, I painted and weathered the existing frame, then stuck metallic vinyl over all the logos and repeated the process. The skull had internal electronics and LEDs that I wanted to utilize so I designed and printed a mount with conductive pads that could interface with the existing screw holes on the case. The mount was wired back to the PC components, delivering power from a USB power line.
The 3D printed mount was not strong enough to hold the weight of the skull by itself, so to reinforce it I cut and bent a metal bar to hold it against the case. I used this image to reference the curve of the bar when updating the 3D model of the mount, so the mount would follow the contour of the bar.