Susan,
From your earlier picture, your chaff ejection slot may be a bit too narrow. You won't know until you give it a try, but to my eyes, you'll need it to be wider.
If you do make it wider, there's a chance that beans will then try to creep out the slot as they are stirred. My solution was to make a little retaining wall at the slot's opening - just a half inch tall - that kept the beans in, but allowed the chaff out. Simple.
Looks like you're well on your way to your first UFO/TO roast.
I've prepared a quick how-to document. I'll see if it will work here. If not, I'll send it to you.
Great work on this project, Susan - as always!
David