Okay...I see your reasoning...don't know how much "wobble" there is in the
camera back but you should be able to tighten the spring clips to reduce it.
In my experience, the only time anything moves is when you place or remove the
film holder or the dark slide...if you're careful, this should present no
problem.
As far as "zero-ing up"...with a 'dorf you use a spirit level (do they call
them torpedo levels where you are?) to check all of your planes to see if
they're level....then you make any camera moves that are necessary. Copying
artwork calls for a camera back parallel to the plane of the artwork...check
both with the level and shoot away.
I live in Chicago...the home of Deardorff and worked at a catalog studio where
they were used exclusively. Not even dozens of underpaid professional
photographers could hurt a 'dorf...built like tanks.

argon