To clamp the pendulum on to its arbor, I drilled two perpendicular holes -- one for a tightening bolt nearer to the end, and one for the arbor a little farther in. Then, I slit the end of the pendulum. Here is the assembly with a 8-32 bolt with washers in place. Tightening the bolt grips the arbor more strongly.
The tightening bolt is accessible when the pendulum is in the frame. Here it is as it is installed.
In order to test the workings of the mechanism, I mounted the frame against a set of sturdy shelves with a clamp.
In this position, I was able to give the pendulum a push and apply some weight by hand to the center wheel. The mechanism appears to run, though some of the gears occasionally bind. Usually, it looks like the fourth wheel pinion is the culprit, but sometimes the third wheel pinion binds. With a small weight attached to the end of the pendulum (a pair of vice grips) and a 3 lb drive weight it will consistently run for about 15-20 seconds before stopping.