Thanks everyone, appreciate the replies.
Some might remember that (like Mike Mazarowski's) one of the Pevensey's arrived built back to front and upside down

And Geoff (Demon) gave me the help to get that sorted out. They ran ok, but never had much power (a slight touch on the flywheel would stop them) but they looked great at least. Not knowing a whole lot on timing engines, every time I tried it just led to failure and I'd put them aside again. I wrote to MSM and asked for instructions, the first set they sent I tried to follow them and couldn't get anywhere. When Geoff read them, he said that they were all wrong. I told MSM and they apologised and said that there were wrong and rewrote them. I still couldn't time them and always had air leaking out when turning the flywheel (there was no position where there was not air leaking out).
My MSM Echuca has always ran well and had LOTS of power. I took it down and took the cover off and noticed that the slide valve was slightly different from the Pevensey's but still oblong 13mm x 10mm, but it was orientated a different way?

??
I took the Pevensey's apart and put the slide valves in orientated the opposite way. After watching heaps of Keith Appleton's timing videos I attempted again to set the valve timing and then small adjustments on the eccentric.
Two TOTALLY different engines now. When turning the flywheels there's two distinct places where no air escapes and two where air escapes and they have power enough that I cant stop them with my fingers. Its been a long time getting here, but I am glad that its sorted out.