The tuner, showing several of the trimmer capacitors
A closeup of the trimmer capacitor. It is about 1 x 1 x 1 inch, and is ceramic. It is mounted in a sheet metal frame at the bottom (notice where it is crimped in place). Inside the ceramic top is a rectangular place, and there is a similar plate attached to the adjusting screw that is moved in and out.
Here is the top view of the tuner, showing 15 of the trimmers. They are mounted to the chassis with a 1/4 inch nut and have a screwdriver adjustment.