Figured this would be interesting to the group:
Several years ago I picked up an "as is" Widget disk from eBay. I didn't pay much, and wasn't upset when it made horrible grinding noises when powered up.
Last night I was fiddling with my Lisa again and recalled a post saying there was a glass graticule inside the drive. I wanted to see how this was arranged, so I opened up the dead disk:
You can see that the head arm is attached directly to the voice coil actuator, and the graticule is mounted in the upper right. Here is a closer picture: