The hoodshape is slightly different.  I can't remember if its 96 or 97 when the new design came out.  Regardless, I've seen early 1st gen Impreza's fit late 1st gen Impreza hoods with no problem.  There is a little gap, but its not significant.
I think I actually made up some cool picture/overlays a while back.  I'll see if I can't dig them up.
EDIT: okay, here we go
1993 WRC car right headlight
 
99 WRC car right headlight
 
The 99 headlight with the shape of the 93 overlayed in pink
