Since you are not trying to break the sound barrier, you would get similar results if you just plugged all the holes in your grille and made the front end as smooth as possible.
A blunt front end can be just as streamlined as a sharp pointed one at low velocities. The ideal shape at highway velocities is a teardrop - not a pointed box.
http://ecomodder.com/forum/showthrea...ends-2914.html
You might take a look at a Kamm back modification such as this one :
http://ecomodder.com/forum/showthrea...evia-9437.html
I see that you shielded the A arms with this design - you'll definately see some gains there.
You could also use flexible rubber sheeting as an airdam, and you wouldn't have to worry about pot holes and such.
Austin eh ? I'll keep a look out for your van !