Why not NARCOA though? That organization has been able to put on speeder excursions on railroads small and big. They have for example done quite a few on Montana Rail Link, not exactly a small railroad. They have been fairly successful in part because they have been able to demonstrate a very rigorous set of safety standards, as well as having (I believe) their own insurance. By being NARCOA certified you would be able to provide anyone that asks (insurance companies, law enforcement, ect) proof of a published set of standards that you maintain your car to, something that’s not just arbitrarily made up by you. I would think that in the event of an incident where the safety of your car was called into question, showing that you follow and are certified to a published, widely accepted and used set of standards would be a good argument in court, should it have to come to that. Plus you would have the added advantage that you could go on a NARCOA excursion should you choose to.