Danno has a good program to follow, the hill climbs and interval training help you make big gains in your training. The final week has you doing a long ride that will give you the confidence you can easily finish the "real event". The key elements to a 60+ ride is proper hydration and caloric intake, with the hydration being the key element. Not knowing what kind of weather you will be riding in consume at least 1 large bottle of fluid an hour, if you will be riding in a hot climate boost that up a bit. I start out with one bottle filled with water and the other with an electrolyte mix. As an example, today was 94F and I went through 9 20oz bottles on a 75 mile ride, one Cliff energy bar and a Subway 6in turkey sub and finished feeling very good. Every person is different so use your training rides to better learn what your body needs in terms of hydration and calories. Finishing a long ride with a sore butt and legs is still much better than bonking. Have a great 4 weeks training and a great ride.