To give the definitive info on these boats,
Yes there were two models of Blagg RIB
The smaller "Bosun's Mate" which was about 10ft and the 18ft "Blagg Bosun"
They were made in England, in limited numbers and subsequently in New Zealand, by Barlow Marine, the company of which I was the Production Manager.
I believe that only one set of moulds were ever made, certainly that was true of the Bosun, although Woody Blagg may have retained a Bosun's Mate mould in England.
We built quite a few "Mates", possibly 20, in New Zealand, but only a few Bosuns, possibly half a dozen, and stopped making them about 18 years ago.
They were both quite astonishing performers for their day, the Mate would run all day at 30knots on 25 horsepower and the Bosun was spectacular with a 90, it cornered like a Grand Prix Motorbike, you could pull about 2 "g" and it's straight line acceleration on to the plane was breathtaking.
The Bosun hull was a brilliant piece of design, and it seems a pity that it never went further. I would suspect that the mould still exists somewhere in New Zealand, if I can get hold of Paul barlow i will find out and post the info