[Skunkworks] How can I proof that another website has plagiarized my content?

My client, a small company, yesterday found out (through a newspaper advert!) that a major institution has basically photocopied a whole page from their website which I happen to have developed. They have asked for my help to proof that these guys are thieves, too bad as they have actually hired lawyers to scare us! The lawyers have given us until tommorow to remove OUR CONTENT, from OUR WEBSITE or we go to court. I need help on how I can proof that we came up with this content before them. It happens to be a very niche product that we sell hence the hullabaloo as whoever has the best content wins. I already have ftp logs, emails, copygator, archive.org any more ideas?