great goal!!!
lots of great advice on training strategies here. there is another angle as well which is how you approach the event itself.
squeaking out a personal best for an hour will mean emptying the tank. the longer you can survive into the effort without pushing over the edge the better. if I were trying this I would choose a place that was the easiest to control the effort and keep it butter smooth. a flat road with almost no pauses or stops would be the ideal. weather that has favorable temperatures and low wind will also help.
lead into the event like a race. train, rest, recover, hydrate, sleep, go