The class-legal centerboard dimensions are in the Handbook, here (page 6):
http://forum.daysailer.org/pdf/dsbylaw3.pdfCCS should be able to tell you whether their board is class legal.
Have you asked CCS directly whether their board will work in your boat? When I contacted them, they were able to tell me that their board would not work in my DSII, so they may be able to give you a definite yes or no on your DSI.
And as Kokko mentioned, D&R Marine has DSI centerboards.