if you want to try to get a good time on a flattish route (Macclesfield) I would say you'd need to do some miles on the road to tweak up your "running economy", find out what would be a sensible target pace, and prepare your system for the repetitive battering that it's going to get
but if you were going to do a hilly one (Buxton) and not worry so much about absolute time, you could get away with no road training