To answer your question - of course you're mad!
But then, according to most people, even contemplating a round the world is mind, never mind what kind of bike.
See the links page for - I think - worldtriumph.co.uk - a British couple rode around the world on Meriden Triumphs, cousins to your Norton. Did pretty well too, but they're both experienced with the bikes and love them.
As for the Guzzi, they're pretty reliable, newer being better of course.
PERSONALLY I can think of much better choices than either - but since tons of people have gone rtw without listening to me, and on everything from 50cc Honda stepthroughs to scooters to Gold wings to R1's, hey, ride what you like!
Just be aware of WHY you're choosing that bike - if it's simply because you have it and you're too lazy to buy something else, well, that's your decision. You have to live with the consequences, not us! If you aren't set on riding one or the other - and if you can't decide which of the two, you're probably flexible enough to consider something else entirely - and I would suggest doing so.
Read the rest of the "Which bike" forum for lots of ideas and suggestions.
YOUR perfect bike is out there.
Come to the UK Travellers Meeting to see a great selection.
See you there!
Seek, and ye shall find.
One world, Two wheels.