I think I did some 30k weeks leading up to it. Mostly just regular training and racing. With EC pushed up and the regular races I wanted to do pushed out I didn't really have any time for long endurance climbing days. I was kind of burned out to be honest.
If you want to finish both days, the single most important thing to train is recovery between back-to-back hard days. A lot of people go balls out on the first day and are dead the second.
The guy who got 3rd in the 3s was in a bunch of races with me this season, and I'm pretty sure he did it on a whim with no specific training. He was really strong though, won a race mid season on a solo break and had the points to upgrade to a 2.