Carbonfiberboy 

My caveats with my previous prescription is that yes, you have to have your nutrition and your pacing dialed. With that in mind it probably is good to do at least one 75-80 mile with similar climbing before the century if you don't already know what to do. Or heck, do an easy 200k and get some miles in your legs. Be that as it may, my standard training for 400k rides was just 60 miles and 4000'. It really is the intensity over distance that increases fitness and endurance. I call it "the ability to repeat." I find that I want to burn all the matches I have. Early in the season, which would be about now, I'll have 'em burned soon after the halfway point, then the challenge is to simply finish. But that's how I get strong. Save the negative split for the event. Train on training rides - leave it all on the road once a week. Going moderate the rest of the time is also training.

I think one 20 mile fasted ride a week is a good idea. That encourages fat burning and makes fueling on the century less of an issue. OTOH, simply riding a lot does essentially the same thing, so it certainly isn't necessary. I did that for a while, then quit when I was doing 2-3 hour unfasted hard rides without eating during the ride simply because I didn't get hungry. So same thing.

Speaking of mileage, a weekly mileage of 100 for a few weeks before the taper for the century assures the ability to finish, barring stupidity during the event. 150 miles/week for those weeks will assure a strong finish. So like 60 Satiurday, 30 moderate Sunday, then 20 moderate 3X during the week, maybe intervals one of those days, maybe not.

Another thing to watch, coming back after a long layoff, is overdoing it. Watch your HR on the climbs. If it doesn't come up to normal levels on the first climb, back it off and keep it backed off while testing on rides until you have a normal day.

On the 3rd hand, I'm an aggressive rider. Not everyone has to be like me. Sure is fun though.