According to John Dobyne’s Santa Fe Boxcars 1869-1953, published by the Santa Fe Historical and Modeling Society back in 2001, the Bx-13s, which were not modified with roof extensions, were the first to be rebuilt in steel. The program ran from 1950-52. The cars were rebuilt with riveted side-panel assemblies and extensions for the ends, which raised the inside height of the cars to 10 foot 6 inches. They were also given new AB brake systems with crosswise-mounted reservoirs, 6/5/5 Youngstown lightweight doors, and either Blaw-Knox or Transco metal running boards. The cars retained their Ajax handbrakes and Dalman I-level trucks. The rebuilt 985 cars retained their Bx-13 classification, but were renumbered into the 32500-33484 number series. These cars remained in service until 1973.
The cars that Prototype Junction are planning produce are the Bx-11 rebuilds. This rebuild program began in 1956 and continued through 1962. The majority of the class were rebuilt very similar to the Bx-13 class and assigned numbers in the 19000-20438 number series. This series retained their Bx-11 class designation. The cars numbered between 19000 and 19895 were modified from 10 foot 6 inch high Bx-11s in the 210000-210960 series. The cars numbered 19896-20438 were rebuilt from 10 foot high or unmodified Bx-11s in the 124000-125999 series. The last of the rebuilt Bx-11 cars remained in service until 1976.
The primary differences between the bodies of the Bx-13 rebuilds and the Bx-11 rebuilds were their roofs and ends. Dobyne states that after rebuilding, all the Bx-11 class had rectangular-panel steel roofs which extended to the ends of the car. The extension panel on the ends formed the peak of the end and included a Dreadnaught corrugation which matched a portion of the original recessed Dreadnaught ends. They were also given sill steps with two rungs at each corner of the car. These rebuilds retained their Dalman 2-level trucks, but the were modified with ASF spring packages. Most cars in this series were equipped with Youngstown doors, but some of the higher numbered cars received Superior 5-panel doors.
Just a comment on these rebuilt cars’ paint scheme. the Santa Fe adopted its “Ship and Travel” paint scheme with the large herald in 1959, in the middle of this rebuilding program. According to Dobyne, there was a break in production between December 1958 and August 1959, so the first car produced in August, car number 19848, was probably the first car painted in the new scheme.Hope this helps!