As I understand (stood) it, the work was taking place at the Museum of Mining and Industry. It's located off I-25 at the exit to the north entrance of the USAF Academy, about 12 miles north of downtown. The academy is to the west of the interchange, and the museum is to the east. When I last visited, the cars were located outside of a shed just east of the main building.
I heard somewhere that they moved the cars to another place to continue the work, but the museum is still worth visiting.