I talked to the Ohlins guys a while ago, the shocks were designed for a Mk5 race series in Japan. The series requires stock springs so this is why these are standard struts, designed to be used with stock springs. DG springs would no doubt work great.
They did mention a customer who contacted Ground Control and purchased a coilover sleeve for the fronts and camber plates, and essentially converted them to coilovers, so it can be done. You could use a collar that takes 2.5" ID springs, and then use whatever rate linear springs you like.
http://www.ground-control-store.com/products/description.php/II=717/CA=65
The shocks can be adjusted to quite stiff, and will easily support double the factory spring rate, which is 225. You don't even need 450 lb springs for good handling, but for a track dedicated car that's the right ballpark.
I have the data sheet on them, but there isn't much of interest other than setup instructions and some initial damper settings to use.
With the conversion kit this would be a great setup.