Regarding originality, I have no qualms about any owner modifying a car to his or her requirements. It's a right of ownership and if others don't share your view, well they can do what they want can't they? I currently own an Autokraft Mk IV and have no problems with changing the engine for something with more power. It's exactly what I intend to do and I'm only following a path set out by AC themselves.
Additionally, one of the issues with time warp cars that still wear their original paint, that are supeficially corrosion free, is that it's often difficult to make good the chassis without taking the car apart. Whichever way you look at it, one day that chassis will need making good, to provide a safe driving structure.
I like to see cars on the road, rather than in museums, so while an original car is a joy to behold, surely it's hampered by its limited usability?