If you can't find the factory data best alternative is to find a machine with the same pitch screw and copy the set-up from that.
If it helps my metric Smart & Brown 1024 has a 4 mm pitch leadscrew, 12 divisions on the dial and uses gears of 12, 14, 15 and 18 teeth. My gears are in a nice bronze and appear to be straight cut at the helix angle of the screw.
It also has a spiffy little plate telling you which gear to use for which pitch and what number of divisions between engagements gives correct alignment of the cutting tool.
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Having sorted out your dial system do make proper rack to store the gears on individual pins with clear labelling of the teeth counts. Its essentially impossible to see which gear is fitted so if you store them loose you will eventually end up trying to thread with the wrong gear fitted! If you have the same set as the Smart & Brown counting teeth to decide whether its the 14 tooth one on the indicator and 15 tooth one in the box gets old fast. I know a man who got it wrong.
Some lathes have a set up with all the gears permanently mounted on the shaft with a pull up and lock feature to select which one is in use. Theoretically better but there can be issues with making the reference line clearly visible at all positions of the dial.
I wonder how hard it would be to do an electronic one. Maths should be easy enough but an effective display clearly showing the approach to the engagement point might be hard. I'd probably go for a stepper motor driving a mechanical dial.
Clive