hmm, now that I think about it, that's actually not what I want. There are only three intake ports on the engine's head, so having three intake manifolds which split into six throttle bodies is really only beneficial if going for max performance, but is total overkill for just efficiency. a simpler setup with three manifolds and three throttle bodies would be ideal, not to mention half the cost for injectors, etc!
perhaps I should just make my own intake manifolds - there is a suprising amount of stuff online about DIY casting! This guy makes his own motorcycle parts:
http://virtualindian.org/3techcasting.htm