Still working on the "prototype" combination coach. I may have some new photo's later today. I've come up with the "wall" between the compartments and the corridor and I'm just letting the glue set up, each section is added to the previous ones.
I've also got almost everything I need cut for the second bank in coach one and a bunch of parts cut for the remaining two. I need to find some vey fine wire to make up the ceiling light harness and finish the modifications to the roof. The luggage racks and sconces can be added later as I am trying to make it relatively easy to get back inside (unlike the way Lionel did it). Once coach one is done, I will open up the brake coach to come up with a design for it.
In doing additional research I came across a video of the Universal Florida theme park ride. The coaches used in that "train" are very close to the Lionel cars, they just dropped the last few feet where the bathrooms would be. Also, that train does not "turn around". They just back it up for the ride from Hogsmeade back to London. The far windows are TV screens and the corridor panels appear to be the windows that have LCD elements that grey out and double as a "rear" projection screen during the ride, aka shadowing Dementors or characters passing in the corridor with appropriate dialog or sound effects.
Built up compartment


Test fit. The floor and side panel are not where the should be. They are being pushed up by the wiring that has to be tacked into place with some "warm" hot melt glue. The roof has to be notched to allow for the transverse panels. I could not do this until I had the compartments built up. I like the way the cloth seat covers look.

