Don't forget about SeatGuru (http://www.seatguru.com), a TripAdvisor company, which specializes in collecting and curating exactly this kind of data. They're not exactly n00bs at this kind of thing…
Seatguru can tell you "the 777-200 config version 1 looks like this", but can't tell you "the flight you're booking will have that aircraft in that configuration". They can tell you that historically it often is that aircraft/configuration, but that's not actually enough to project forward into the future with full reliability.
And that's the hard part. It's even worse for the more common case of domestic flights, because those get swapped way more often than long-haul international.
And that's the hard part. It's even worse for the more common case of domestic flights, because those get swapped way more often than long-haul international.