Hey HOn3 folks, please excuse the cross-posting, but I think I found a partial answer to the "slats-on-the-outside" issue. Here's what I posted on the HOn30 group.
"Speaking of stock cars, check this out. I've been wondering about the outside slats on the upper half of the D&RGW stock cars for a while now. EVERYBODY can understand why slats should be on the inside (animals push on the inside, so putting slats on the inside makes sense). Check this out http://www.drhs315.org/blog/drhs-railcars/stock-cars/stock-car-progress/
The folks of DRHS did a restoration on a couple of stock cars, and they did a marvelous job of documenting each step. Some of the pictures show something shocking--the inside slats go all the way from the bottom to the very top of the car, BUT the outside slats are only on the upper half. Put another way, the upper half of the stock cars are...DOUBLE SLATED!!! My guess: the outside slats were strictly meant to act as letter boards, and would never be touched by the livestock, as the inside slats took all the beating from the pigs and sheep.
I would love to go and take a look at every stock car that the D&RGW ever had, and look inside to see if the inside slats go all the way up, but unfortunately, I live too far away. Perhaps we could put the power of a larger group to work. If anybody lives close to a museum with one of these cars, let's put this mystery to rest--look inside and tell us what you see!!!"