Thanks for the link but I had already seen that one.
The image is wrongly captioned. It is actually a Bristol Mercury (although the file name suggests a Hercules), which looks a bit different. (see images of Hercules further down the page).
Not much different, but I want to try and get the appearance as close to correct as possible. I think the main difference is that the cylinders are longer in the Pegasus. This is a good example of the need to check sources. File name "Hercules", image caption "Pegasus", actual image probably a "Mercury"!!!
I had another wild goose chase to the Solway Aviation Museum. Rumour had it that they had two Bristol Pegasus. One was given to the ATC in Scotland, location unknown. The other was in very poor condition and has been cut up as a source of metal for melting down and making parts for other engines which are being restored. I think both came from a crash site. So at present I'm still looking.