There is an intake manifold for the 2.9L OHV, but it isn't cheap and they come from the UK. I got one from Ric Wood's operation -
http://www.ricwood.com - and Burton Power offers one -
http://www.burtonpower.com - too.
If distance and cost does not stop you, these manifolds take either three Weber DCNF downdraft carbs or three DCNF-like throttle bodies from folks like Jenvey.
I can find a photo if there is interest.
Yet another downside to this manifold and lots of carbs is that to properly tune an engine fitted with this arrangement is that you'd probably want to or need to stock up on primary chokes (aka, primary venturi), main jets, and air corrector jets. You can then tune the carbs based on what the engine demands or can put up with.
There is a high 'cool factor' with this arrangement, but tossing a fair bit of $$$ to get there.
I'm slowly heading there with the 2.9, and doing lots of R&D with a few loony pals, and getting away from the anemic 2.8, which even after lots of mods is still a POS for a serious road racing attempt.
I hope this helps.
MW