The more I started to look at this prototype photo provided courtesy of Bill Lane (Thank you, Bill!) of the one surviving GLa, found in New York, the more things I started to see. These are details that are visible when operating the car on the layout, especially if you know what to look for. So, I decided to add them as best I can.
The first thing I did to start detailing the hopper bays and doors was to add these angle iron reinforcement strips on the outside of the bays. I made mine out of scale 4" styrene angle strips.
Studying various prototype photos, I placed them angled in the direction such that the "open" face of the angle is facing down. After the glue had dried, I used a razor blade to cut their ends flush to, and at the same angle as, the sides of the bay.
However, no matter how many photos I looked at that showed those strips, there was always one in the upper section that was facing in the other direction. This I modeled also. I tried to see if it was related to the side, such as "Is it always at the A side of the car, or always at the B side?". There didn't seem to be any rhyme or reason as to why one of them was facing the other direction. It is little details like that that you start to see the more you study the photographs.
Next, I started to focus on the doors. There appear to be door stiffeners along the inside edge of the doors. I simulated that by gluing a scale 3" strip of styrene right at the edge of the door.
If you look at Bill Lane's photo above, there is a heavy, thick bar that connects the two bay doors on each side. The more I looked at the photo, the more I think it is shaped like a flattened-out "Z", rather than a solid block of steel. It is riveted to the doors, and the locks at the end hold it in place when the doors are supposed to be closed. The interesting thing is that in the center of the car, that Z bar deviates to get around those door reinforcement strips. I literally spent two days thinking of ways on how to model that. One idea was to use a heating device and a wooden form to bend the strip of styrene to that shape. The other idea I had was to just make the strip out of three separate pieces and then shape it. I had already decided to make mine out of a solid strip of styrene, which is a compromise (I did this because the door locks will cover the ends of this bar, so the fact that it is solid will not be seen from the side). However, when I put the car on the track of the layout, and looked at it from my normal viewing angle, I realized that the center of the car's underside, where this bend would be, isn't really visible. Looking at the S-Helper Service (GLd) and the River Raisin (GLf) cars, they used a simple straight strip of material as well. So, as is my standard in this project (if it is not visible, I am not going to bother modeling it), I punted on the idea, and just cut a solid strip of 5"x5" styrene, cut away a bit of the door reinforcement strips, and glued it in place, as shown below. The bars only cover the actual door sections, so the ends were trimmed just shy of the ends of the bay, and at the same angle as the bay sides.
The other subtle thing I noticed in Bill's photo were the hinges for the doors. There are two of them. I modeled those with strips of 3"-wide styrene. Note the one in the front, right in the photo. It seems crooked. After I saw that in the photo, I went back to the model to double-check, but it is nice and straight. I have no idea why it was distorted in the photo (the one on the left also appears somewhat crooked); all 8 of them are perfectly straight down.
The hinges have a reinforcement strip near their tops, so I simulated that by adding a one-foot long strip of styrene that I glued on top of the main hinge strip.
The final detail I wanted to add to the bays were the door latches. These are rather complicated things to model. You can see one up close in Bill Lane's prototype photo above. I tried to approximate that by cutting a bunch of identically-sized pieces of 0.030" styrene, and shaping them as shown in the photo.
These I then glued to the bottom of the bays in approximately the orientation, in mirror-image to each other, as shown in the prototype photo above.
I wanted to add a bit more vertical detail to the door latches, so I decided to just add a semi-circle. I cut some discs from a piece of scale 6-inch diameter styrene tubing. I then cut those in half with a razor blade, as seen in the lower left-hand side of the photo.
After gluing those to the door latches, I am left with this. One could really go crazy with designing something like that in a CAD program and then have them 3D-printed, but for me this is good enough to indicate that there is something down there, without spending a lot of time super-detailing that part. It took enough time as it was already doing 12 of these!
This is a more normal view of the bays from the side. I think it looks convincing.