Q: What is the coupler height used by the prototype?
A: The centerline of a prototype freight car coupler is allowed to vary between 32 1/2" and 34 1/2" based on how heavily loaded the car is. Couplers on passenger equipment are specified a bit higher at 35".
Q: Do Sergent Engineering couplers provide more realistic coupling distance than traditional knuckle couplers?
A: This answer requires some a definition of realistic coupling distance first. Click here for in-depth information about coupling distance.
Q: How big is the draft gear box on the prototype?
A: First, the term "Draft Gear Box" is a modeler's term, not a prototype term. The prototype does use "Draft Gear", but this gear is not installed in a stand-alone "box" as is often the case with our models. The figure below shows a typical prototype draft gear and its installation modeled by the Accurail® box which is included with our EN87 couplers. This drawing is a top view of what one might see looking at a flat car before floor planking is installed.
This drawing is an annotated version of a drawing that was provided in 1922 as a typical application of Miner type A-18-S2 draft gear installation. The drawing was created to highlight how Miner's draft gear was adaptable to existing "typical" freight cars of the time. Even though this drawing comes from the 1920's, it is very similar to same arrangement used today. Do realize that this doesn't hold for cushion draft gear, which is a different ball game.
A couple of things are worth noting here. First, this whole assembly is built for strength because it has to deal with the force of pulling an entire train. That's why the assembly is built as part of the center sill. This is an important fact if we are to accurately model the "draft gear box" because it shows that our box should certainly be no wider than the center sill which turns out to be 20" across the U-Channels (0.230" in HO scale). You will be happy to know that the width of the Sergent Engineering supplied Accurail® box matches this dimension very well. You might be saddened to realize how the draft gear box you currently use compares in this respect.
Second, see if you can locate the coupler centering mechanism. You won't find it here because there isn't one! Those springs in the draft gear aren't there to center the coupler, they are there to keep the train from ripping apart as it accelerates and decelerates. The coupler shank has a ball shaped end not evident from the drawing that is fits against the plate at the end of the draft gear. The key allows the coupler to move side to side within the yoke housing and that movement is really only limited by the distance between the center sills.