Tom, the head-end cars are from a variety of origins. The RPO is a Rivarossi car with a few added details (steps, grabirons, and some clerestory ventilators). I also added the windows on either side of the baggage door: they were taken from an Athearn coach, if I recall correctly, and the car is a pretty accurate model of the real 7776. The wood-sided express car behind it is a shortened Athearn Pullman. The sides are Evergreen passenger car siding, and the doors and underbody are scratchbuilt, with some commercial brake gear parts used. It was done from a photograph and is quite accurate. The trucks are the original Athearn metal ones, and the car rolls about as well as a brick.
The third car, an Express Horse Car, is a modified Rivarossi heavyweight coach, built using the same general techniques as the previous express car. The underbody is pretty much stock, although the stock trucks were move closer to the car ends. Except for the underbody details, an accurate representation of the real thing, which was used primarily for transporting race horses. The last express car is another modified Athearn Pullman, built similarily to the previous Athearn car. On this one, the windows, which were covered over in the 1950s (the car siding was redone, so the car looked as if it never had windows) are from Grandt Line, and the trucks are Central Valley. There's a more detailed explanation of the techniques used to do these (and many other) cars here:
kitbashed headend equipment
The last two cars belong to Professor Nutbar, and are unmodified offerings from Rapido.
Wayne