While not definitive, the Dennis Kirk 2011 catalog (pg. 604) shows stock replacement fork tubes for the 06-07 FXD as 25.5" and for the FXDWG as 27.5, plus others with various under and over sizes. Believe your 2010 FXDC would have the same 25.5" as the FXD.
My Dyna service manual gives instructions for removal and installation, but no dimensions.
Hope this helps.