I worked with these guys in the past on a huge/complex aluminum transmission casting that was almost as big as a Fiat 500. http://www.deltaresearch.com/

They are not cheap, but they will do small-run stuff. They work with a small pattern shop (their name escapes me), who worked with a company that 3D-prints the casting cores, and then sent it all to the foundry, then Delta machined everything afterward. 4 companies involved in the final bill, but there are benefits in this particular chain.

The pattern shop had software to model the thermodynamics of the foundry pour process against the cores, cope & drag, This is not so much to accurately capture the part’s geometry, but more to ensure that there is good metal flow throughout with no cold spots, knit lines, etc -- which minimizes the # of practice pieces. Based on the pics of this manifold, even though complex to us, it’s a fairly simple part – I’d be surprised if it took more than 2 practice pours (and the 2nd one would probably be usable). And when it’s all finalized, they get more 3D-printed cores and knock them out pretty easily. Cost benefits of the high-tech process will be realized in getting thru the initial R&D pieces with less waste, production run pieces might be a bit cheaper, and you could flip the switch and get another batch 5 years from now that would be identical.

So if you guys are serious, put your research and investor hats back on, and get somebody to offer up OEM pieces to get laser-scanned into a 3D model.

But be aware – the 3D cores have a nice surface finish, and these manifolds will look *much* better than the originals.