The springs you found probably won't work. Eibach is currently prototyping a 1.6" kit for the AWD 300C which they claim will be out in June. I would wait for that kit if I were you -- it'll be done right.
In fact, one of the guinea pigs for the AWD eibach springs goes to my local dealership sometimes (Tustin)... his car looks beautiful in terms of wheel gap AND yet also has the "AWD" on the back - two things ya don't normally see! It's sitting about .6" lower than a stock RWD.
So, it's not just vaporware -- there ARE guinea pigs out there and it's worth waiting for so your car doesn't turn into a ball of flames with some other spring set. Lemme see if I can find some pictures someone posted a few months ago of that guy's car.
Ahh yes, here we go... by the way, according to 'turbohips' in another thread apparently this guy with the test car still had to cut the springs from Eibach a few coils to make the gap look the way it is. Hopefully eibach will get it right by the time they come.
See this thread for more pictures:
http://www.300cforums.com/forums/exterior-modifications/4551-promised-awd-22s-lowered-post51032.html