The headlights on a s1 have more rounded corners compared to a s2 which are more square so the panel beater would have changed the bonnet too as it isnt the same, you would need to do the full swap at the same time for it to work. the diference can be seen in the following jspec links
http://www.j-spec.com.au/list/index.php?ID=8677
http://www.j-spec.com.au/list/index.php?ID=8807