Bill,

The diagram for the B-50-27 class is available at:
https://harley-trains.smugmug.com/UPFreightDiagrams/Box-Car/

It states an "all welded" underframe, as well as having info about the trucks, hand brakes, etc.  The cars kept their wood running boards thru the late 1960s.
The reweigh station you mentioned was likely G.I. for Grand Island, NE.
All yellow lettering on BCR cars was applied by UP from July 1947 to September 1961.


Hope this helps,
Dick Harley
Laguna Beach,  CA