Thanks for the info on that web site, I had no idea that they were still around. FYI patents expire after 17 years, and that manifold has been around for a lot longer than that. So I don't think there are any patent issues to worry about. I've also done a patent search and found nothing current.
Since the 351W intakes have a water jacket passage, I doubt that they would fit on the adapter. Just getting all the various 351C intakes to fit will be a challenge; with all the high port versions of the 351C heads out there, many of the adapters will have to be custom machined to fit a specific intake. This limits the 351C manifold interchangeability, of course, which is one appeal of the intake adapter. Some of the advantages will remain, of course...