The reason for doing all these things isn't relevant (GCR and Imberhorne) It is the achievement of major projects against the odds that is the point. Not sure about the origins of the WSR triangle, it could be for NR as well, but useful for the WSR.
If the units have to run with alternative power due to new regulations so be it. 100% accuracy is often impossible so, compromises have to be made. Alternatives to coal for steam locos are being investigated, not ideal but, needs must. A 4VEP on the Ardingly branch is incorrect but, appearing at Haywards Heath isn't. The only historically accurate answer there is to get it back on the main line. The 4SUB 4732 and 2BIL 2090 were used on the main line for a few years. The heritage movement will continue to do the 'impossible', no matter what some say.