Since it is a steady you don't need super precise dimensions except for the bar spacing, which is 40 mm. From memory the spindle is offset 10 mm towards the front - I'm sure of that. I don't have a note of the spindle height, but if you put something flat across the bars and measure the height to the point of a dead centre (or any bit of bar machined to a point) you can get a ruler measurement and do the sums: 6 mm + thickness of flat + ruler measurement. That should be accurate enough.
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Somewhere I have a drawing showing the positions, but I can't find it right now. I think I measured the height sing the method above, but put a known diameter rod in the chuck and measured with a digital caliper, then did the sums.
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My SL is now in Australia, so I can't check the measurements, but I'm sure of the 40 mm bar centres and the 10 mm offset. I must sort through my DB/SL drawings and get them in some sort of order, weed out the duplicates, and put them in the Files.