So, er, lots to digest here, thank you!
I've had a rough go at @Flying Pig and @The Johnster's suggestions to shift everything Eastwards a bit, to see how it works and check I'm understanding it correctly. This creates the headshunt, towards the Gas Works in the Cranleigh prototype. I'm guessing freight would either arrive from the Horsham direction and 'wrong line' into the siding, reversing back as necessary, or arrive from Guildford, run around, then as before. Looks fiddly in real life but probably quite fun in 4mm.
Arguably you could push the whole thing further East to leave some of the platform 'off scene', use the footbridge (if it wasn't obvious, the blue blob is a footbridge!) as a scene break. Might be a bit odd having the east-facing loco 'off stage'…?
I think the downside of this approach is losing the level crossing and Knowle Lane, which I've got some connection with (a sad incident in Mum's Mini Metro pulling out from what's now a car park Sainsbury's loading area and in the model will be the platform exit/line to Horsham) and the back scene of Cranleigh High Street… equally rotating it 180º would lose the village setting I'm quite keen to retain. I suspect at the very least I need to get the tape measure out again and see how much space I've got in total. Things to ponder on before I start building.
Thanks @AndyB – I've got a copy of the Branch Lines book, which is good for setting the scene, and I'm getting lots of ideas for prototypical rolling stock from shots along the line. I've also got the Pryer Signal Box Diagrams booklet, and have been raiding the Bluebell Railway photo archive! Very few pictures in colour, unsurprisingly but somewhat unhelpfully! Also agree the sidings are probably over complicated – I think I'll remove one of the sidings around the Goods Shed, which will provide a bit more space for loading/unloading/turning lorries.
I like @stivesnick's backscene mounts. Will definitely investigate those, as making the backscene removable definitely resolves the access challenges for the return loop…
@Innerhome I think the shift and creation of a long headshunt should remove the challenges of shunting on a tight bend, but I clearly need to do some practical work on the off-scene curves to make sure they're not a derailment waiting to happen. On the fiddle yard, this is definitely the least developed area so far, but I suspect creating an additional scene isn't going to be a runner – saying that I might operate it like a terminus (ie consider a platform with run around + some sidings) for the 'play' value, but without dressing it up as such. That said, an earlier sketch of the fiddle yard area did include a turntable to avoid doing the 'crane shunting'… but I suspect all of that will come out in the wash.
Thanks for reading, and thanks for the ideas… I can see this activity is in danger of becoming an addiction already…
Robert