Wow, I thought this thread was long dead! I can bring you up to date: The friend showed pictures of it to Bonhams in London, and their first reaction was very enthusiastic. The item was sent up to them, and gradually their interest cooled. After a while it was found that this was in fact a much later copy - expertly done and with a great deal of effort to provide a false provenance, but nevertheless an outright fraud! As others have noted, the lettering and some of the spellings aren't right for the period. The real killer is that there are a number of other identical fragments floating around the world. Sorry if this is a disappointment to any of you, but maybe there is a warning to others. I still think the idea of these diplomas is interesting, and I learnt a lot from the experience. Fortunately the friend had paid very little for it, and he has now kept it as part of his "hard lessons museum".
This fragment is in the Israel Museum, Jerusalem, since 2002. You will see that the bottom right quarter corresponds almost exactly with your fragment. It is difficult to figure how another diploma of the same series could look so different, and in the same time have the same line breaks. Your fragment is the work of a forger who is good at creating old bronze patina but not very good at imitating Latin script of the late 1st century. Very interesting fake indeed...