Mounting the motor like I had it before worked, and it's even quiter. I also took another pass at tidying thing up inside the box and on the main breadboard. To position the dispense sensor on the wall of the box I had to cut away a bit of the funnel so it doesn't block the sensor. I'll have to show this in more detail later because it's how I'm rodent-proofing the peanut stash. The hole the peanut drops from is out of reach and the funnel slope makes it difficult to get any footing to jump. If a mouse crawls up the dispense chute they won't be able to get to the peanuts.
Once I have things back together I'll try it out and upload a video testing it with various objects.