Yep - familiar with the terrain - did 100km (starting at Queen Elizabeth Park and going toward Brighton a couple of years ago). As long as its dry, then should be ok (i wore trail shoes then, but a guy i ran with wore regular running shoes).
There's a couple of steep bits, but walking is the way forward - trying to run up to save time is a false economy IMHO.
Need to start upping the miles (whilst I'm still grinning from the PB at Wokingham half yesterday)
*heads to marathon training schedule section of website*