PRR GLf - Prototype Information
There was only one GLf car, road number 250000. It was a PRR GLa hopper car whose side panels were replaced with the bulging ones and whose height was increased by 8 inches, all to increase the carrying capacity of the car by 15%. The car used the 2D-F8 truck. The earliest known photo is when the car was in the Altoona shops in February 1935 (see below), and it appears to have been removed from the roster in July 1951. Prototype photo scanned from photo owned by Peter Vanvliet.

Pennsylvania Railroad Steel Open Hopper Cars, page 144+, contains a full description with two photos.
Tracing drawing and prototype photo.
All GL-class hoppers' technical info.
Larger photo.
Prototype photo available for purchase.
Prototype Information