I am also searching for Johan Dewalt Ledermann. I know he arrived on the ship James Goodwill from Rotterdam on Sept 27, 1727- "With Dewalt on the ship James Goodwell were Michael Tanner, Ulrich Stauffer, Peter Zug, Christian Miller, and Hans Longnecker."*
I think there might be some new research that shows they were from Saalstadt, Southern Pfalz, but have so far been unable to verify that.
Are you aware of there connection to the German Baptist Church aka Dunkards? - "Daniel(son) organized a Brethren congregation meeting in homes in the Little Conewago(PA) area west of and around later Hanover by 1738. This congregation, according to Durnbaugh, included Eldrich, Dierdorff, Bigler, Greip, and Studtsman families. His father may have preceded him as religious leader there."*
* Quotes are From:"Monocacy and Catoctin" Vol. I, p. 176-178