I did the L-B ride two years ago with no training and being a smoker with poor cardio health (run up the stairs and nackerd) at the time, and i didnt find it too hard, just take it steady and drink LOTS. Stop at every rest stop to fill up and hydrate.
You have already taken a step in the right direction, you just need to keep it up, and get your diet in line.
It might help posting what kind of daily routine/eating routine you have.