Ended up doing something similar to Dan’s topic, and created a quick sketch with partially constrained dimensions in Fusion360. Just searched and cannot find anywhere, I probably didn’t save 
Vaguely recall @Jonathjon mentioning something similar to Mike’s simpler straight forward approach…
Just double checked docs https://docs.v1e.com/lowrider/#initial-squaring, content looks a bit light on exactly how people should calc pulloff after diagonals are measure to be skewed?
Don’t remember how @jamiek calcs Skew compensation. Guessing he (or someone…) has a web hosted OpenSCAD based Table Skew Compensation calculator that’s linked, or within the LR4 Calc page, currently, or in the future 