Mark, it gets very complicated because of the way SCARM displays tracks and objects. However, for your purposes, check the property values for the L-Girder rails. You didn't attach the SCARM file, so I can't check myself, but I suspect the vertical position and height fields are not correct. The lowest track (blue) is "0" elevation and the decking is 1/2", so if you want to portray a 1x4 L-Girder rail and have it display beneath the bottom level, try changing the vertical position to "-4.0" and the height to "3.5" (or post the SCARM file and I'll take a look).
The 1st photo shows where I added two beams, both 3.5" tall. The one on the left has values of "0" and "3.5", the one on the right "-4.0" and "3.5". As you can see, the one on the right is properly displayed beneath the track whereas the one on the left is displayed above the track. The 2nd photo shows the 3D view. Once properties are changed for all the rails, your L-Girder should be displayed below the track. Let me know if that works.
Now, please note that the beam on the left is not beneath the Yellow track even though the elevation of that track is 8" and the beam is only 3.5" tall. I first noticed this when I tried to add an object below the tracks in a design I was working on and I had the tracks set to their actual height of 40". I could add a shelf at the 8" point and get it to display correctly in 3D, but they always covered the tracks in 2D. My simple understanding is that tracks are displayed as a singe "object" without regard to elevation of individual tracks and are displayed on top at elevation "0". Therefore any object with either property value set to something greater than 0 will always cover the tracks regardless of track elevation. As you might have figured out, a vertical position less than 0 will display beneath the track and that's why the "-4.0" fixes the display.
