This was among the parts I was given a number of years ago from the wreckage of one of my uncle's B-17s. Most of the parts I was given I could identify from the numbers stamped in them, but this one remained a question. A friend who was a B-17 flight engineer thought it might be a servo for some part of the auto-pilot system, but I just saw an image elsewhere of what was identified as the gyro for a Norden bombsight, and it was very similar to this. Unfortunately I only have this one image of the part, which is about 4" across if I remember correctly.
One of the other parts I was given was the remains of the mount for the bombsight, so I know they had the bombsight at some point.
Any bombsight experts out there who can tell just from this image?