The climbs: this is a vert race, plan for it
Scout Mountain is a climber’s course at every distance. The 24-miler still asks for about 5,600 feet of gain, the 50K around 7,400, the 50 near 10,800, and the 100 stacks 21,000-plus feet of climbing into the day. The summit of Scout Mountain near 8,686 feet is the recurring high point, and you earn it. If you treat the early climbs like flat running you will be wrecked long before the hard part. Hike the steep pitches with purpose, keep your effort even, and save your legs for later.
The footing is real mountain trail, high and remote, and the altitude alone takes a bite out of sea-level lungs. Get time at elevation if you can, and if you cannot, respect that your climbing pace up here will be slower than it is at home and plan your splits around that, not around your flatland fitness.