This project has evolved over on HMEM, apologies to the guys who frequent both sites.
Basically my project is a reversing horizontal twin loosely based on My Westburys design, an example, which I believe belongs to Don-tucker over at HMEM.

Mine is destined for a large side wheel paddle steamer called the PS Pevensey which still operates today out of Port Echuca, australia largest inland river port. She will be 7'6" and radio controlled which poses a few issues for a steam engine.

And the scale plans...

The changes to the design are simply making the cylinders level, mounting them on either side of the boiler cover (more on that later) and making the crank a stand alone pylon type with 4 individual pylons, 2 in close next to the throws and 2 out wide as this will a long crank shaft.
I am a caster of metal so it was decided early on to make and cast the components and this thread is my journey so far... yes it would probably have been easier to use billet... but where is the fun in that?
Ill go through this quickly with a few pics per post... to break it up... firstly I have Mr Westburys plans but really dont refer to them much, its all in my head. To make this a sloooow revving engine set Ive increased the bore size from 19mm to 25mm (3/4 to 1 inch).... on with the show!