Thanks Brino, and sorry for my lack of clarity. I know the banjo, just can't figure out how it all fits together. I have never seen these weird segmented rods before, with the machined ends that appear to go nowhere. Granted, I am an absolute novice with machinery this old, and painfully acknowledge that it will be slow going. After seeing the knob picture, it makes more sense. I have a few random [to me] knobs with threaded internals. Thank you for sharing that. I'll poke through more old lathes on there and see what I can glean.
I put the leadscrew on and found the bracket that holds it near the headstock. The half-nut fits that like butter. The other rod I mentioned is like a short clone of the leadscrew, but beat to s--t. Must have been a screwcutting or change gear component that someone really laid into.
The gear that the carriage turns on the long track is tiny and chewed up, but the action is still smooth. It is small enough that I think another can be made easily.
Optimistic as I put this together that it has some life left. I'm seeing evidence that it was dropped once or more, but the critical components are still solid. I need to braize on another tooth on the long track under the bed, and whip up some of the 'consumable' parts like gears.