Cool - thank you.
That's how I wound up wiring it myself in the end - by some amazing fluke, I managed to get that bit right
In the end, (with help from herby08) it turned out that ignoring the previous wiring on the Leetro, and figuring things out based on the labels of the laser-power-supply itself worked.
Ground=G
TTL=TL
PWN=IN
Though I'm guessing other people's power-supplies might be different.
The other issues I had:
1) X motor going left when told to go right : Fixed in the 'Manufacturer's Parameters' by reversing "Datum" and "Key Direction"
2) mis-scaling between software and hardware: Fixed by changing um/pulse. I found the correct one by looking in the old Leetro syscfg.ini - although the LaserCAD 'Manufacturer's Parameters' do provide a way of working this out if you get stuck