I`ve tried to find a way to stay with my Workflow using Freecad for Developing and Path creation. But there are not postprocessors for Marlin in Freecad. So I decided to run grbl on my GT2560 Rev A board. The first try was with the setup from John Boiles and it looked good but the steppers didn’t moved. So I took a deeper look and can now present a commit with correct pin mappings to run grbl-Mega-5x.
Its late and I need some sleep.