If I had oversight at the FAA, and all this is correct I'd turn up to paint out the reg and just orphan the aircraft - then charge them for the privilege!
I need to re-brief myself here as this is slightly outside of what I normally deal with, but, as there is a weight limit above which you CANNOT EVER be part 91, you can be private ops but off the top of my head it's Part 122 whatever the subtext if you're blindly adhering to 91 you're breaking the law. That 73' must be close to the MTOW limit for the regulation.
This sort of thing really pisses me off as it leads to the needless and over regulation that simply blights the professionals in the business.