Just been playing around with some bits of paper after having comprehensively re-read the narrow gauge book on Calshot. This sketch doesn't sound that feasible given the right hand hangar will scale down to 36cm wide. (Not 50cm as I originally said) Alternately, the castle can be on the left hand side.

I'd ideally like to follow the prototype as close as possible, in the next few days I'll have half a dozen NG wagons to play with which will need to be modified to resemble the real things.

We'll see...