Wow, that sounds like fun. Your sprints are a great start, as is Mr. Furman's circuit.
Overall, when it comes to sport-specific endurance, there's nothing like doing that sport. I know it's hard to find training partners, and in their absence, you can just repeat the event around a heavy bag. It's not the same, but if you stick to the schedule, you can at least have some mental experience with that ordeal. The determinism of the event reduces the stress. I practice spar with my friends and usually outlast them all. My opinion is that only part of that is physical conditioning. The rest is teaching your body what it must do. It's kinda like running without a known endpoint. The records skips on and on ... but really, I think there is a lot to be said for prior event experience.
As you probably know, you will lose a lot of water. It's a good idea to drink enough beforehand, preferably with some of that Nuun salts. Other sports drinks are more for recovery and their acidity will turn your stomach. Sometimes, the dehydration get out of control and the chills set in. I wish I knew more about how to prevent or mitigate that.