My guess would be extending the slots for the gunwale clamps to reach the sides of the NED?  The Sassafras is pretty narrow at that aft location.  Or shave down the motor block to lower it a bit because the NED gunwale is higher?

I have a NED and I just clamp the Newport motor to the boat with a few spacers under the gunwale. The motor has excellent rotation and tilting, so I don't use any special mount. Ping if you want more info.

   I bought the same mount, excited to use it.  I learned that, after trying it out, it's not wide enough to mount far enough forward to avoid the motor contacing the rudder.  I played around with the idea of mounting it on the bow, and with even building a motor case to mount it forward of the dagger box.  I also considered building a new rudder that integrated a motor into it, but bailed on that because it would be terrible for sailing.  I even considered an add-on angled bracked on the transom.  Ultimately, I decided that the NE dory jusy ISNT a great boat for a motor, which is what Jon Harris has said repeatedly.  I decided what I actually wanted for motoring and sailing was a Goat Island Skiff.  The Jimmy skiff would fit the bill as well as some other flat-transom models (Tenderly, perhaps), or the much different SW dory.