Couldn't you take like Edelbrock Magnum head or whatever ported it out to a 290 cfm and make a mold from the port and then do a full on job even if it breaks through everywhere using epoxy etc.. to make it work for the 325-330 cfm port make a mold of that add a certain minimum thickness around that, use the 290 mold as cast and make a cnc program to port out to the second.