If you can't set the scale on import then you can fix it afterwards... You can group the imported geometry [if not already grouped] and scale it manually... If you know exactly what size one object should be then edit the group and with the Tapemeasure Tool pick the two points on that object [might say 400mm in the VCB] and then immediately type in the correct size + <enter> [say 4mm] - you are then asked if you want to scale everything - say Yes... Everything inside the group is scaled [you can do the rescaling to the whole model but only use this IF there is nothing preexisting that was the right scale already...]