As a builder of 2.5" scale equipment and also wanting it to be able to interchange, if necessary, with 1.5" scale, I stack two 1"x2"x1/8" wall tubes as coupler pockets. The lower pocket is set for having its coupler centered at the IBLS standard of 4.38". By default, the upper pocket is 1" higher, making it 5.38" which is only 1/16" variance from the "de facto" and ostensibly negligible in practice.
I plan to have some of my rolling stock at the DLS meet to display and for sale. I'm currently building some East Broad Top hoppers and flat cars with Vulcan trucks. My website isn't up and running yet, but should be in a few weeks. I have an ad appearing in the Sept/Oct issue of Live Steam. Look for the "Wright Rail Works" ad paired with an ad for Solidesign.
Adam Wright