If you are the kind of guy that likes old bikes , then simply buy an old Brit bike and use it .
I'd go for a simple old bike like a BSA B33 , or maybe a RE Bullet .They are not worth too much and are reliable if treated well . If you are a real masochist ,you could try a Panther .
See "The Last Hurrah " ,which is a story about two New Zealanders who took a Panther and a Norton from NZ to Holland .Bits of it are on youtube YouTube - The Last Hurrah: PAKISTAN and there is a dvd and book .
Don't take a Commando ,they are too long a wheelbase to handle well on the rough and the frame is not very substantial ,plus they get hot when travelling slowly.
The only thing I have against the modern Bonnies is the weight ,which is about 100 lbs more than the old Bonnies .This could be a factor if you travel off the highway and will have to pick your bike up regularly .

One of the new fuel injected Bullets might be OK ,but they are rather expensive .
An XS 650 Yamaha is OK if you like classic Japanese bikes and want to travel a little faster than a single will go , or maybe an old Moto Guzzi ,yeah that would be a blast .

Whatever bike you take will need good preparation and you'll need to be very familiar with it's complexities and idiosyncracies but for some people ,like myself , that's all part of the fun .Plus you have to factor in the people you will meet who want to talk to the interesting guy on the wierd old bike.[ or should that be "the wierd old guy on the interesting bike " ?]

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