I have been out on bits of the course and it is good fun, challenging but not going to kill anyone. Some typical coastal path. I have not seen the whole thing but I will be down there racing it this time.
Well, if you have a good understanding of your fitness levels through previous training you will be best placed to make a call but I don't think you will find an effective way of replacing running completely as training for a running event. Other activities are good for complimenting it or aiding recovery but I don't believe they can be used as a full time replacement. I would suggest you do whatever you can that is pain free to keep yourself in some form of training and prepare yourself for a tough day out adjusting your race goals to suit your fitness on the day.
Good luck with your recovery and hope you make the start.