You are definitely right, there should be some attribution back to the Katana project. The license seems to state that a copy should be provided and the modified files should clearly carry notices. I am unsure why I didn't think of the licensing impacts when I did this work. I could alternatively redo the implementation without using anything from the Katana project if you would prefer that? Probably not much of a choice unless the license is changed to apache, which I would assume isn't an option.

Sorry for not thinking so far ahead; Licensing was seriously the last thing on my mind when I made these changes!