Hi, GLC! I looked at your intro in the "Getting to Know You" thread. You said you were already in great cardio shape when you got your road bike. What did you do before cycling? 110 miles in 2 days is a pretty big ride -- easily as or more difficult than one metric on a weekend. How did you feel after? If you felt good and didn't have problems with feet, chamois, eating, etc., you probably just need to build on that base -- and not even much unless the century has significantly more hills than the MS ride.

I'd listen to the tips about getting through organized rides comfortably (like ride your own ride, eat, hydrate and use the portapotties regularly). Sign up for a metric or two between now and then just to get more experience with the whole organized ride scene and you'll be good to go. Listen to your body and be sure you fuel/hydrate early since it will be a longer ride than normal and you can't play catch-up in the heat, but you'll have plenty of time to acclimate to it in 12 weeks.