The thing about transcontinental, non-Interstate drives is that there are literally hundreds, if not thousands of possibilities, and since you are deliberately avoiding the major cross country highways, you end up stringing together a number of different good regional routes. In your case what I'd be looking to do would be to use US-64 across northern New Mexico, US-54 across the Kansas, US-50 in Missouri and Illinois, OH-4 to work my way north a bit, then US-6 through Pennsylvania and MA-2 across Massachusetts. Of course, you'll have to find suitable connecting roads to join that all together, and leave at least 2 or 3 more days that an all-Interstate would drive, but that's one basic routing.

AZBuck