This is a quick explanation howto trace model lines in SketchUp. There are many ways to do (such as measuring all dimensions and building up the part from scratch) but this time I found this technique pretty effective.
Since the original model was very well made I only had to remove unused lines (the model consisted only of lot of triangles) and to simplify the contours. First I selected some key lines from the original model:
and copied and pasted them to another location:
Then I marked the middle (because the parts should be mirrored later which saved me half the work) and cleaned up the lines (meaning, combining lines and erasing unwanted steps in the construction which would be extremely hard to build). This leads to that:
You can clearly see a much cleaner model to work with.
A bit more done:
And the model as it looks at the moment:
I'm aiming at a length of about 35 cm which should give a nice display piece. Of course the result can be up- or downscaled to suit your needs.