On my first trip to the Alaska Range my partner and I chose a rarely climbed Alaskan Grade IV+ (6,000 ft+, 90 degree ice, rock to 5.
. My friends that had been to the range suggested something easier saying "Nobody does anything significant on their first trip to the Alaska Range". We trained hard all winter climbing technically difficult, big (5,0000 ft+) routes in the Cascades all winter and we made a sucessful, rare ascent of the route.
We learned everything we could about the route and found an extremely accomplished and well traveled climber who attempted the route the year before. (Jack Tackle and Doug Chabot said the route was much harder than they expected). He said the crux rock band was too difficult to free climb with packs and would either have to be aided or packs would need to be hauled. We did neither and pulled overhanging roofs, crampons scratching rocks, packs tugging us down. We both fell seconding pitches, but we did it.
My point is, learn everything you can about the route, take heed from experienced climbers, but don't let the doubters get you down.
Now, here is my advice:
Fully acclimatize by climbing the West Buttress or Messner Couloir. Before arriving at 14k you will need to decide how you will approach the base of the Cassin. You have several options:
-Descend to 11k and approach via the NE Fork of the Kahiltna Glacier, A.K.A. 'The Valley of Death'. This is the least technical of options, plus you can cache all of your technical gear you don't need on the West Butt at 11k, however, the route is threatened by seracs and crevasses.
-From 14k descend the West Rib to the base of the Japanese Couloir. This is one of the quickest routes but is more technical. I have watched EXTREMELY talented and accomplished apinists turn around due to poor snow conditions.
-From 14k descend via the 'Seattle '72' ramp described briefly here
http://colinhaley.blogspot.com/2010_06_01_archive.html (scroll down to the bottom).
If you haven't already, contact Joe Puryear, Mark Westman, and Colin Haley (contact info in previous post). Nobody currently climbing has more Alaskan Range experience than these three and they would be happy to give you advice about the route, gear, bivi sites, etc.
Training by toproping 40' waterfalls and snow shoeing around the White Mountains ain't going to cut it. You need to train your body and mind and develop the skills for climbing big, hard routes, the likes that you have never seen.
Make as many trips out west as you can. The Canadian Rockies or the Tetons are probably your closest venue. (Colorado doesn't really count - no alpine climbing to be had, keep driving). Climb big waterfalls and alpine routes. Hone your systems for climbiing in extreme cold. Closer to home practice rock climbing in crampons and a pack.
Improve your fitness by trail running and lifting weights. Include long slow distance, intervals e.g. running hill repeats, and lactate threshold training (tempo runs). Once a week do a long hike (4000+ ft elevation gain) with a 50+ poound pack. Dial your systems for winter camping. In the weight room focus on upper body, core, and leg strength.
If you make smart decisions and sincerely aknowledge you and your team's fitness and abilities the worst that is likely to happen is you will summit via the West Butt then get a look at the Cassin and decide to come back when you have more experience. Or you may just send the rig.
Best of luck,
EB