Updated 7/11/2019:
Today, I am tackling the horizontal supports for the Pennsy cross-section. Here's the latest (hopefully correct plan (drawing). Track centers for parallel tracks in the straight sections are 3.75" apart.
OK, so here's the actual. In this photo, I am positioning the horizontal support for the masonite that will hold the stryofoam scenery. The carpenter's square shows a depth of 3" from the top of sub-roadbed, but it will be 3.25" to account for the depth of the foam.
This photo shows a test-fitting or mock-up of how the 1/8" masonite fascia will mate to the benchwork (bottom) and the cross-member. Width should be a uniform 18". I used a piece of cardboard to stand-in for the masonite.
More when I know it.
George