Start spinning some miles. Your going to use muscles your not used to using. Your ass will hurt in the seat as well. Time in the saddle. Watch what you eat and keep hydrated. You don't want to "hit the wall" or some call it "bonking". You just might learn what it means though. Trying to stand from sitting in a chair will be very difficult. Also cramps come from lack of hydration. Don't schedule your jobs too close, you'll need some recovery time. Your talking about work that usually requires heavy equipment. Green logs are always so light till they dry out and get heavy.. keep a close eye on things as your going to push the limits of everyone erything. Anything breaks you'll need a plan "b". Maybe a backup bike and trailer, or stay on great terms with your friends that might have something you'll need in a bind.
Take some pics before, during and after. There will be people that will call bs without pics, and if things are indeed like you mentioned, you can show off things with the proof in the pics and reflect on times later on.