I think to truely be called a historic replica, the car needs to be of the origincal construction and materials as what we're trying to show. So to me that means wood sills, body built to an original configuration, and interior using materials not compatible with normal tourist trains. Obviously this is something the Friends could do to reproduce a San Juan looking train.
Between the current 0292, 0252, and 0452 cars to get to that state will mean a complete teardown with all wood replaced. Which means you are effectively building a new car. Maybe you can save the metal work. Not unlike the 'Grande's practice of jacking up the car number and replacing everything else on the car.
In my mind, I've rather have a ratty looking 053 that I know has most of the original fabric as constructed instead of a pristine looking couch replica that mostly looks like an original car, but was completely rebuilt in 2008. Guess that's why I worked on the 0579 and not the 0306.