Maybe you might want to develop the idea proposed by Pilot Developments years ago, when they were asked how they would get something the size of Flying Scotsman to pass under the M11 motorway, if the engine was to run on the Epping-Ongar line in Essex. Pilot thought the best way was to - in their words - "hinge the stack", so that it would swing away from the smokebox in order to gain the clearance necessary.