Like seemingly everything in its fleet, the Pennsy had a large number of class GRA gondolas. The cars were built early in the 20th Century (between 1907-1916) and many managed to hang on into the 50s, with over 2,000 still in service in 1952. I covered these and other PRR gons in my Hindsight clinic (details posted here.)
Robert W. Smith's two-part article about these cars and the related class GR, "Pennsylvania GR-GRA, Variations on a Theme," was published in Mainline Modeler, February and March, 1990. It contained drawings and other useful details. Be careful with the drawings as I know one is captioned, "MODIFIED WITH AB BRAKES" for a drawing of car prior to upgrade with AB brakes!
I built a Westerfield kit years ago and loved the model (photo above). However, the kit I bought and built was more of a spur of the moment purchase and it had stake pockets on the sides, a feature not common on cars in the early 50s. Recently, I saw a kit without stake pockets on eBay at a very modest price so I decided to take the plunge. Here is how I built it.
As with any resin flat kit, I ensured that the sides were of the same length. With that accomplished, I glued the basic box together as shown in the photos. It was important to get the tops of the sides to match the tops of the ends. Mission accomplished. The accompanying photos show the basic box from the top, bottom, and side, prior to the addition of the floor/underframe. The floor/underframe were glued top-to-bottom and sanded to fit inside the carbody. The castings contain quite nice detail on both the exterior and interior. Given that the largest surface is wood, there is ample opportunity for weathering.
For the sides, I changed a few details. For the straps in the two end panels, I used 0.005" styrene instead of the cast resin pieces. For the towing loops, I created them from 0.015" brass wire, but opted to remove the kit's nut-bolt-washer detail and added discs punched from 0.005" styrene using an RPToolz punch and die. For both these discs and the straps, I will go back and add rivet detail after the model has been sandblasted prior to painting. The pressure retaining valve is a Precision Scale styrene part wit 0.008" wire. The sill steps are Yarmouth Model Works etched metal parts. The trucks, as shown in the photo below, are Sunshine Models 2D-F8 prototypes, with Reboxx wheelsets and Reboxx journal inserts that dramatically improve the rolling quality of these trucks.