What are the main dimensions of the chassis ? I've more interest in things
Western than Southern, and wondered what prototypes could inspire the
platework. From what I understand, it's a nice simple chassis that is easy
to build and runs well.

CAD-wise, I've got a copy of RoboCAD here and can export DXF files from
that. However, I'd not claim to be experienced in tech drawing, so I'd want
second pair of eyes to check I hadn't made any glaring errors.

What parts lend themselves to being laser cut ? Obviously the frames,
external rods & hornguides are early candidates, but could the cylinder end
caps, water pump eccentric strap & rod, valve eccentric strap & rods and
eccentrics for both also be done this way ? I'm looking for a model that
will be fairly quick to build, so the more modern accuracy that can be added
before I start the better.

I do have access to CNC routing machines capable of producing brass
platework (similar to Polly Models & ModelWorks), so this side of things
could also be speeded up somewhat.

Simon.