Give it a try but be careful. There is real opportunity to hurt yourself if you ride too far, too fast. Many good posts about only increasing mileage X% at a time you might want to search for.
Also, if you are not comfortable riding with a group give some thought to your strategy at the ride start. A big ride can be pretty hectic and you certainly don't want to crash or burn out trying to keep up with the wrong group.
I'd rate this one as risky, but if managed correctly, the downside can be controlled.
Good luck - I'm sure you'll give us an update. I've got some friends doing this one and it sounds good.