That manifold is not a easy one to reproduce.
To make it competitive you have to do a 1 piece cast, machine it then.
The first part will cost more than you are willing to pay.
How do i know. Used to teach cnc programming
Thats why my instructor said to have a casting place take a look at it. Found one in Tampa. So we'll see what that have to say. I need to make an app't and get over there with manifold in hand, of course there will be some changes to it, no vacuum port, bore will be slightly larger than stock, and rail length will be a bit longer, and have a inside radius instead of those sharp corners, plan to make the flange area a bit thinner too, by approx .030 for an easier install. Closer to the design of the Nemesis