It's been a couple of days mostly waiting for tiny bits of paint to dry... and some musicing. Finally everything is coming together. The case, or whatever you call it, is finally in place as is the ladder. I added a small washer before the signal arm so it sits 'in the middle' of the case nicely. When all folded up (for the umpteenth time) the arm turns nicely, just tight enough not to wobble but free enough for a servo to drive it. 

There's no base with the kit so I've chopped up a bit of plasticard for one as this may improve the chances of survival with Royal Mail. The post will stick through about 10mm to locate it on a layout, the ladder will glued in holes to provide at least some rigidity. The maximum height of  the signal, i.e. the plan, is defined by the length of the ladder. From the instructions with the stop signal kit it seems ladders should be at 120' to the platform, thereby determining the distance of the bottom from the post. It's a very long time singe I used a protractor!

The lamp isn't fixed yet as I need to double check the height before doing so, and get access to drill the hole for the operating rod. The loop on the operating crank is hidden behind the signal arm itself, so hopefully there won't be a strange shadows. I've decided against giving it a butt, mostly in deference to GWRiness (according to the drawing).