Alan,
Thanks for pointing out those lugs. Once I'd separated the boiler from the running plate, the lugs were quite visible and I didn't need to resort to the saw. One lug was unfixed and the second had a thin trickle of adhesive holding it in place. Some gentle levering of the cab sheet with a jeweller's screwdriver and it too was free. It was then a simple matter of sliding the cab off the boiler as you've described, fortunately without any damage.
I'm not surprised about the handrails. Fortunately I've plenty of Alan Gibson scale replacements in stock!
Andy