Did a little bit of filing/cleaning stuff up, and then added some control rods for the “gab hook” valve gear.
Those rods extend from the top of the smokebox over the boiler to the top of the firebox. Isaac Dripps’ drawing of the John Bull as-built shows these controls being mounted on the sides of the firebox, but the present location is the top of the firebox, which seems to make more sense - perhaps Isaac misremembered their location.
This engraving of a train on the Boston and Worcester line of 1835, interestingly enough, shows the rod for lifting the gab hooks routed over the boiler as well. Strangely though, it seems the engine crew have jumped off.
If you want a demonstration of how a locomotive like this would be operated, here’s a video of the replica Planet (a contemporary design built by the same people who made the John Bull) in action, and with explanations: