Yep does sound like an awesome trip. Here's a few random thoughts fwiw.
Not having done the drive to alaska, whats the weather like in April going through BC? Any chance of delay's (if that matters). Does the ferry company have an equivalent to standby flying? If you're already going to be in Seattle is it worth checking out?
No affililation, but check out http://denver.craigslist.org/pts/1568617106.html
he says he has a gas tank from a 78 with no leaks. Or maybe possible to just get a few jerrycans if they'll fit in the back? Or maybe see if there are any yakima roof boxes for cheap on CL? Then toss the light stuff in there and gas in the back...
I dont have any cruiser parts that would help but I'm sure I got tons of old derailleurs and chains in my black hole of bike parts.
Of the three climbs you mentioned I've only done Whitney, your adventure makes me wanna "postpone" the job and load up the cruiser and go adventuring.
'97 lx450, 170k, factory lockers, ome 850/863, 285's, 4 working doors(1 more than the old fj55 )
'74 project pig (sold