Well, I've determined that there is supposed to be a spring at the heel of the shutter lever. Remove the film spool clip at the bottom right of the camera. This reveals a hole through which you can thread a screwdriver to remove the pivot bolt for the shutter lever. There's a recess to the right of it where a spring belongs. Your classic "ball point pen spring" is the right size, I cut about a 1/4" length. My mechanism now works well.
Other notes. I decided I needed a small thrust washer at the top of the pivot shaft. Not so much to reduce friction, as to move it downwards a tiny bit. I was having trouble getting enough clearance for the swinging hood on the back of the lens, it was catching on the pivot bolt of the shutter lever. That, and a little force with pliers, got the clearance.
There presently aren't any leather flaps at the ends of the swing, there's residue that looks like there may have been. Anyone else with a No. 1 want to let me know if they have leather flaps there?
So the mechanism is working fine, now I'm just figuring out the right size, shape, and folding for the new bellows, which I'm making from rubberized nylon changing bag cloth. Thankfully I have a No. 3A with original bellows to look at how they did it there.
Then I presume I'll have to put onionskin paper across the film plane to fine-tune the focus. I presume one normally focuses it at 20 feet?