Welcome to Ribnet!
As you say, unusual. Mine (albeit the smaller / narrower beam version) became the 5m/ 2m beam O-Pro but via being called the Attaque in between. Maybe at that time Humber named the wider beam version with a differnet name?
I called Humber to find out what I had just bought & it's transom capacity. Sue was really helpful . Might be worth giving them a call / email.