good that the spindle goes both ways.
Mine would jog the axis without a computer attached, gert daft question time, can you turn the pot on the control panel 1/2 way and try again, try with the manual button on
also check the fuses in front of the stepper drivers, (i doubt they will be blown, but its worth checking to knock another potential issue off the list).

The stepper driver manual is available online, download it as it shows how they are wired.

Limits looks like someone's borrowed a part or 2 off the z limit, the black switch just behind the chuck and in line with the top of the z axis is your z limit switch, on top of the axis are a couple of holes this is where the limit switch adj rod fits Yours seems to be either invisible or missing. Operate the switch a couple of times with your finger as they some times get stuck, on the righthand side of the front your lathe is a hole with 4 3mm threaded holes around it, there should be a plate with a switch on it, which allows you to jog off z if the limit switch is on. Don't worry about that now i put it there as i might have forgot to do it later.
If you remove the Boxford plate on the l/h front side it will give you access to the limit switch wires, and the wires for the index and position wires
Don't connect to pc just yet, as it's better to check things work, It does look like someone converted it in the past what to your guess is a good as mine.
let us know how you get on especially after you move the pot,.

My boke i fely dirty when i converted it to -ve earth and fitted an old jap reg/rec i found in the shed, put some better coils on and cried when i fitted a boyer ign kit