What makes a 6500 series flat an automobile car? I thought that it was just the addition of stakes and canvas to cover the cars. Reading through "A Century + Ten of D&RGW Freight Cars" I stumbled upon another difference that I never knew about. It seems that 8 metal cans with lids were added at various points along the car. One at each corner and four in the middle to allow two autos to be strapped down. Inside the cans are chains to strap down each corner of the auto. The cans extended down below the deck with the lid flush with the deck. During Railfest I had the opportunity to take a look at one of the remaining cars. Five of these cars existed and one of the others is now at the Colorado Railroad Museum.
Here are a couple of shots of one of the "cans" on car 6529 (I think).
Dave