...so, I'm giving each of you a point.
Thanks for that, Otto!
I saw the Auctioneer's catalogue entry online, as well as various other (post auction) references and photos.
I don't remember David Baldock having it but I'll have a look back at his adverts.
When it was with von Raffay, is was called a 40/60 and there's no way a 5970cc double-piston engine could ever have been rated a 12 CV.
French fiscal CV, like UK RAC horsepower, seems to have been bore-based so my 75mm bore 4-cylinder Mors is 12 CV (or 14 h.p.) (and is 2120cc) - perhaps Ray B. can remind us how the French calculation went.
When Bunny Tubbs needed to register his 40/60 Gobron-Brillié (for the first time) in 1946 he did so in Surrey where they used the normal HP= N*D^2/2.5 ((N)umber of cylinders; (D)iameter of cylinder) even for the double-piston engine, whereas London (where he lived) had a 1.6 divisor, not 2.5.
That would have made it 47 hp, not 30. as he reported his engine to be 110 × 110/90 = 7603cc, by the way..