The concept is pretty simple, if you are going to do 1+ hour climbs then do longer and longer sweet spot intervals as I mentioned earlier. Here is an example of say picking a day (Tue or Thur or Sat) and progressing out the length of your intervals:
Or just go out and ride outside with longer climbs or sweet spot work. A good goal is to work up to an hour or more, to align with your projected climbing times. I was probably 2.8W/kg when doing the Death Ride, and my easy “aerobic endurance” climb-all-day-pace resulted in slow climbing times but loads of fun and no problem finishing: Monitor West 1:20 (1 hour 20 minutes); Monitor East 1:45; Ebbetts East 1:53; Ebbetts West 0:57; Carson 2:11 (those were all heart rate paced, and it really was a leisurely pace).