I am fairly sure that the Ron Whitten book has the timeline of the company structure at about this time. I dont have the book on me but as a fairly rough guide I am fairly sure it goes something along the lines of the following:
Peter Thomson (no P) and Michael Wolveridge became design partners in the 60s, designing mainly in Australia and Asia. For a period in the 70s and 80s they did some work with Ron Freem (this may have been mainly American work, I am not sure but the Whitten book will tell you). In the 90s Ross Perrett's name went on the company after he had worked with them for some time. Wolveridge left the partnership a few years ago and the company is now Thomson Perrett.
I assume you are in America, I would hazard a guess (but could be completely wrong) that Ron Freem would have been largely responsible for the masterplan, unless the plan contains numerous pot bunkers and references to ha-has. Then it is likely that Wolveridge was responsible.