I ended up doing this ride twice this season. Once solo from north to south and another time with a small group for RATPOD Unlimited. The ride from south to north is actually a bit harder with more climbing. That said the biggest challenge is the route finding. I think if it was easier to find this route, it would become an instance classic. Follow the strava gpx closely. This is one you want to download on your gps device before attemping.
You ride on hwy 200 to Gold Creek Road. After 9 miles or so you hit a large climb, that is the biggest of the day. From there you head behind a gate for another 15 miles of what I call “Pain Platuea.” Eventually you come out of the gate and have nice descent and rolling section in to Seeley.
Seeley to Missoula, https://www.strava.com/activities/3550197202
Missoula to Seeley, https://www.strava.com/activities/3646466592