I could think of several reasons Private Cars wouldn't work. One the highest sleeping car number I think is 24 passengers most are lower. Each car has a different charter price some are as low as 1,000 a day some are upwards of 5,000 a day. If you want to charter coaches there aren't many single level coaches I can think of five off hat that are certified. Plus each car is different interior, and furnishings. So some people who get a coach ticket in say St Augustine will end up smelling that funky smell in the Exploded smerth. While someone who gets an IP coach gets something similar to a long distance coach on Amtrak.
Plus you would have to get a train manager to get everyone together I could think of three qualified people who could do that fairly easy.
That is the locomotive guide for PVs with train length restrictions for the CZ.
I would really love to see slightly more of that guide because I've been very curious about the current train length restrictions at different stations (for instance, on the LSL route...) But I don't know where to get a copy of it, is it available AARPCO members only? :-(