I'm a little confused about what you're after. First you say you want a new bike built from currently manufactured components to put in a time capsule that would be really appreciated in 100 years time. THEN you say you want classic looks.
I'm pretty sure ANY bike you build today will look "classic" in 100 years. Sloping top tubes, odd shaped aluminum tubes, and unicrowns are actually more representative of these times than round steel tubes and lugs are.
So what are you going for? Something to represent the best that 2008 has to offer in 100 years time, or an "instant classic" that will bring the best of todays technology to a bike with "classic looks".