Not exactly true, Josh.
The F&CC Box Cars were built to the same ACF Plan as the D&RGW cars and they used a 4'0" truck. The C&S Box Cars were also built to the same plan (even before the D&RG cars were built) and they had a 4'0" truck.
In many cases it was what the company called out for. In the D&RG's case, it was a 3'7" flat top arch bar. In the C&S and F&CC's case it was a 4'0" Equalized diamond arch bar. Both types of trucks had inside hung brakes.
Also, remember on the D&RGW 30' reefers that the lower tonnage capacity had to do with the fact that the Ice Bunkers, with their wooden walls and metal lining also added to the TARE weight and thus subtracted from the Capacity of the car. This is the reason given for the Long D&RGW Reefers, as they would haul more than the 30'.
Rick Steele