I did it on a BMW R1100GS. 5 days, 22 hours and 43 minutes. IBA Sanctioned. Would I do it again, I would answer no, I have no desire to do it again.
As for prep, just make sure your bike is in good running condition, be prepared to ride in mud, dirt and gravel. If I was to do in on a C-10 I would invest in some front and rear highway bars. I do not think the C-10 is the best bike for this ride because of all the gravel, dirt and mud, but I know it could do it because I saw several Harleys riding the Haul road and they made it.