Doug,
There are plans for the "Chama" fleet cars that the RR used to build them with. They were prepared by an engineering consulting firm. I saw copies of them in the Antonito enginehouse in 2000. The drawings I saw showed the interior framing. There may have been external plan view drawings as well. Earl probably remembers more of the specifics. I sorta doubt that any of these plans heve been made publicly available as they were proprietary drawings of the consulting firm.