The match plate is cast aluminum, Bruce.  By the way, there is only one; the photo shows two different sides of the same match plate.  The master pattern was machined from some kind of plastic, and from that a mold is made for the match plate, and the match plate is cast from that mold.   For the first five manifolds, I will be keeping a couple of them for reference (so that I can measure them and compare them with future castings), and I figure I'll screw a couple of them up doing the machining as I'm developing the programs.  I also have to cut one apart to look at the water jacket, and make sure that area has a lot of integrity and that I don't have any porosity or leakage issues.  So the first five intakes won't be for sale; the manifolds for sale will come from the production batch of 50 that I hope to order in mid-June.