This isn't Trev's event, but the following may be of assistance...
The tracks around Mallard's pike are good, bit of a hill on the longer adidas trail, but the corresponding downill is fun..
Not sure of the details of he cycle route, but the Forest of Dean is pretty hilly. Any sections alo the severn or wye will be fairly flat, but any section in the Forest itself will have a few hills. These hills tend to go on a bit. Therefore practice hill climbing and descending