Andy Carlson writes, on this subject:

....the only
keepers are the 12 panel 10'6" 40' boxcars, and then, only the 6' and 8'
door, diagonal panel roof versions. I don't know of any prototype 7'
door car, and SF, D&RGW, and GN cars seemed to be built late enough to
have utilized only the diag. roofs.... I am going on recall only, and
others >are certainly encouraged to correct me.

Okay, I will. The Santa Fe's Bx-48, Bx-50, and Bx-51 classes (a total of
2,500 cars) were all 12 panel AAR cars with rectangular panel roofs.
Diagonal panel roofs first appeared on the Bx-53 class in 1949. Though the
models have obvious shortcomings, C&BT kits for 12 panel cars with
rectangular panel roofs are the only way to accurately model the Bx-48
through Bx-50 classes.

Richard H. Hendrickson
Ashland, Oregon 97520