Thanks! Just to be clear, it's a 403A (not a 401A). So no built-in camstack.
It's weird to have a screw left over when I had all the screws needed to put all the parts back on. I'll take a look at the parts list/diagram.
I never would have tried tackling this project (or even buying a vintage machine in poor condition) if I hadn't found the wonderful AndyTube series of videos on YouTube. All hail, Andy!