The big ones are not bad bikes for long rides.
A guy I worked with rode from NJ to the west coast, picked up his wife who flew out and did a tour of the western stuff, then rode home (solo).
He started out with 100,000 miles on his bike and had no issues other then a cracked aftermarket exhaust mount.
No motor work was ever done to the bike, but he did put in a 6 speed trans.
Still, I would rather do it on a more sporty bike....I think.
I did the same thing on an old Triumph (1979), but I was a lot younger.