Hi Mike,
No, arc movements are not implemented in the old morgan marlin fork. It is probably going to take a lot of work to get the old marlin running it, and I personally don’t work on it any more. The only two machines I have running Marlin is in the Morgan display in the showroom…
All of it is implemented in the new Smoothieware firmware though… If you need those movements, I recommend getting a Smoothieboard or Smoothieware capable controller.