Get used that Rallye lying down......I did it on an 1100 some years ago and it very nearly broke me
Seriously, it's an epic ride and you'll find it tough in places on the 1200 but you'll manage it as long as you take your time. Just for info, there are road routes around if it gets impossible and I always tell people that discretion is the better part of valour on a long trip.
You'll be wet in Tennessee and Mississippi, hot and dusty in Oklahoma, scaling rock strewn peaks in Colorado, blown away by the stunning landscapes in Utah, boiled in Nevada and releived to finish in Oregon
Looking forward to following the trip.