Cool, another dez racer!
Everyone already gave the best advice. I remember my first dez race. Everyone thought it was funny that I was drinking so much water the day before and the morning of the race. It worked! I never crashed so much in my life on that 52 mile loop. I would have been so much more sore after the race if I didn't drink water like I did. Take a couple of asprin before the race and that'll help too.
Don't even worry about the gas. My KX500 made it the entire 52 mile loop with a little to spare. 3.4 is plenty of gas.
I treated my first one like a long trail ride. I believe your H&H's out there don't have long bomb runs like we do out in Lucerne Valley, Ca., but I did extremly well to the bomb run and was one of the first in my start to the bomb, but fell when a guy in front of me stopped in a tight rocky canyon section after the bomb. My bike flooded and I could not start it to save my life. Seemed like everyone passed me. After I got it started, I had to get back on to the trail as I was off and on top of big rocks. I fell about five more times in the space of about 50 yards trying to get off those big rocks. After that, it was okay since I no longer had to deal with dust. I finished pretty far back but had lots of fun. I did have a 4th gear get-off in a sand wash when a big rock jumped in the sand wash as I was comming. I landed pretty far from my bike but nothing happend to me or the bike. I just had a helmet full of sand the rest of the race.
Sorry for the long post. I just had such a blast my first dez race. I was the worst riding I ever did, but like I said, it was a blast. IMHO, its the best kind of off-road racing there is. Have fun and be safe!
BTW, run Dunlop 739 Desert ATs and you'll never have to worry about a flat, especially if your running a 18" rear wheel.