This is a quick job - about 90 minutes design build time - so the detail is poor, but the overall shape looks about right to me. I hope you can use it as a starting point.
Start with a block 1.5" x 3.0" x 7.5" (I used a cut down 2x4), 1/4" dowel for the axles, and 1.5" hobby lobby wheels (or make your own).
Glue the pattern to the block (red line along the block edge) then drill the axle holes (9/32") and cut a slot for the windscreen with a 1/8" kerf table saw blade (I stuck a piece of 1/8" BB Ply in place for the windscreen).
I used a band saw to cut the side profile (my EX21 can't take the 3" width) but your Hegner might take 3".
Tape it back together then cut the top profile (cutting off the fenders).
Cut the outline of the left side fender (the one with the picture on it) using a scroll saw. I hand-held the shape so the picture side was horizontal facing up.
Us the left fender to mark the shape of the right fender. Cut the right fender like the left fender.
Cut the axles and put on the wheels.
Fit the fenders around the wheels. I used an oscillating drum sander to shape them and clean up the cuts a little. Glue and hold in place with rubber bands until the glue sets.
For trim, you could add something for head and tail lights if you'd like. You can also add a 5th wheel to the trunk lid. You might drill out or paint the interior, or you could cut out the door openings then add the doors back.
One thing is that the front wheels are within the fenders but the rear wheels stick out. You could cut out some space in the body to let the rear wheels tuck in better.
If you make one, please post a photo.
