Your trick with white parts looks pretty. It's definitely a step in the right way because it uses real 3D engine. However, (again 
) I cannot recommend using any 2D software for any enhancement like deleting unwanted edges. You need to find another trick how to force the 3D renderer to do it for you.
An idea (I did not test it): make parts have the same color as their edges; old parts white, new parts yellow. Then you should get a silhouette of last step parts - and that you can filter in 2D software to get an edge of the block. Shouldn't this work?
) I cannot recommend using any 2D software for any enhancement like deleting unwanted edges. You need to find another trick how to force the 3D renderer to do it for you.An idea (I did not test it): make parts have the same color as their edges; old parts white, new parts yellow. Then you should get a silhouette of last step parts - and that you can filter in 2D software to get an edge of the block. Shouldn't this work?