Regarding engine removal: way back in the thirties Morris Commercial made their double decker bus so that the complete front axle with radiator, engine and transmission could be wheeled out as a complete unit which seems a good idea to me. Of course back then it was an overhead (or high?) cam petrol engine so probably needed more regular maintenance like decarbonosing for instance? I assume that nowadays rear engined busses will have a similar set up.
Pete.