Most of this was sadly guess work. However, you were correct with my using boxcars. I found a boxcar in game that closely resembled one I had and was able to use that to build my units as close as possible. Not perfect but it worked. Haven't been able to finish the layout sadly. Had some stuff come up in 2019 then Covid messed things up for me in 2020 so the layout is still in limbo.

did you use it for the curve radius, too?

nvm just now seeing the boxcar thingy

how did you measure?