A service-bay display works when the viewer can see the access opening you chose. Opening every panel is not necessary, and it can consume space without revealing anything from the normal viewing position.
Choose one visible job
Cab access
Face the open door toward the viewer and leave its swing clear.
Engine access
Make the documented engine opening the focal point; keep scenery out of that sightline.
Tool change display
Show the fitted and spare tools distinctly, without implying undocumented compatibility.
The M318 85956 has documented cab and side-panel access. Use its actual opening direction as the starting point. Do not infer an opening panel from a molded seam on a different release.
Lay out the bay from the viewing position
Place the model on a plain removable base first. Look from the height and side where the finished display will normally be seen. Add a wall or equipment prop only if the important access remains visible. A camera at that viewing position is a useful way to evaluate the layout before fixing scenery.
Keep the model’s normal removal route clear. The door and panel clearance are not necessarily the same as the space needed to pick up and replace the model. Avoid attaching scenery to an opening part.
Choose a stable resting pose
The 315 inspection-based review separates useful opening features from sample-level pose-retention problems. A maintenance composition does not require an arm suspended at maximum height. Use a naturally stable pose and leave unsupported movement outside the scene’s premise.
The finished result should have one obvious focus, visible access and a clear removal route. If the detail can only be seen by reaching into the bay and moving several objects, simplify the layout.