A bit of an update on this. I couldn't get the rotary valve to seat sufficiently in the end I went for the plunger type valve from ME article.
(http://i.imgur.com/kHXQeW3.jpg)
And mounted it vertically in the cab floor as its too long to go on the manifold where I had the rotary valve.
(http://i.imgur.com/SNG54kn.jpg)
I also modified the drain cocks so they vent forward and not down or sideways. Down picks up a lot of rubbish from the track bed especially at ground level and sideways is a bit inconvenient for bystanders, especially on a raised track
(http://i.imgur.com/ALVcFuh.jpg)
In hindsight that decision proved itself to be a good one when starting off for the very first time the jet of water can shoot 10 feet ahead of the loco.
The decision to go with the steam operated drain cocks has also resolved a problem that I'm beginning to think was the cause of the state the loco was in when I took it over. The crossheads, bushes and pins were all seriously worn out. When I first ran the loco with the manual and automatic drain cocks it knocked to some extent. I'm guessing that as the original steam drain cocks had never worked the previous owner had replaced them with four individual manual drain cocks. They would have bee impossible to operate on the move so could only be opened when stopped and closed prior to driving off. That would never have got rid of all the condensate water and hence the loco would have knocked. I'm guessing that auto cocks would have this problem to some degree as once the regulator is opened and pressure is applied they will close regardless of whether there is water still in the cylinders. Remotely (steam) operated drain cocks give the driver full control and they can be held open when pulling away ensuring all the water is ejected the cylinders come back up to temperature
This short bit of video with me opening the drain cocks (and blow the whistle) for the camera as I go by.
https://www.youtube.com/watch?v=aq8ePsbRBR4
Pete