I live at sea level, the elevation was not a problem. For ride simulation I did 5 centuries (Feb, April, 2 in May, June) and the last one two weeks before was 60 miles above 6000 feet and 10,000 feet total climbing. But it was the training rides on the flats - long sustained efforts on the flats, into a headwind, and lower cadence - that really helped build the foundation.
Except for lunch I would keep moving. My moment of truth was stopping at the lunch area the second time, before the rollers to Markleville and the base of the 5th climb. Eating a second lunch and meeting up with a Wed night worlds guy was what I needed to have the confidence of doing that last 2.5 hour climb. That was the only climb with traffic and we had an intense headwind in the canyon from Woodford to Sorensens/Picketts Junction (5.5 miles of the 14.7 mile Carson climb). That first section of the Carson climb also has no shoulder - good times at ~5mph 
- so be thankful its not on the new route!
I started at 4:40am and the first almost 10 mile descent (Monitor East) down to Highway 395 was truly epic! Great tarmac and averaged over 35mph without pedaling. Sun was up and low on the horizon, it was a little chilly (low 50s) so I spun my legs a few times to keep them warm. Temps for the day ranged from 41 to 93.
Seriously you can do the entire route, stay on your training and you’ll find its more mental than physical.