Place cameras to their holders. You want the up looking camera lens to be 4 to 5 cm from the table top surface and the down looking camera as low as the holder allows. The distances are not critical. Do not fully tighten the set screws in the holders.
However, make sure that you can tighten the holders so that the cameras are tight without using excessive force. If not, use a layer of smooth tape around the camera body*. The intention is that you can adjust how easily the camera turns in the holder so that at some screw setting, it stays in place but you can still adjust it when calibrating the machine. Once done, you can then tighten the screw to fix the position without changing the adjustment.
Using double side tape or stickers, attach the LED ring lights to the holders.
*: A note about Chinese manufacturing business: It seems to be rather difficult to buy the same exact item again from China, especially when the item is considered to be a commodity. At the time of writing this, I’ve bought three lots of cameras. The store I first used is no more, and even though the description and appearance of the cameras are exactly the same, it seems that the “10mm outer diameter” specification is rather loose. Also, the USB identification string are slightly different.
I don’t think the dealers can do anything about this either, and at my volumes, I don’t get to speak the manufacturers directly on all items. I’m not too happy about the situation, but I hope you agree the above to be a reasonable workaround.