Tim O'Connor wrote:

Chew on this - most PS-1 ends after 1950 had welded mid-seams. But NOT all of them. The
Southern Pacific riveted B-50-37 "PS-1" box cars built in 1955 also had riveted mid-seams on
their ends. 

SP piggybacked onto a C&O order for riveted 50-foot double-door box cars with PS-1 ends and underframes. Each road got 200 cars. The cars were built to C&O specs (Class B-34) and SP got the same cars. One reason for this was that SP wanted gussets at the lower door opening corners, and P-S would not modify the "standard" PS-1 body. But since the riveted cars were not "standard," the gussets could be specified. (See my box car book in the _SP Freight Cars_ series, p. 379). 

Tony Thompson

tony@...