I can trace back the Plonka line to Valentin Plonka born 1862 in Taczanow-Pleszew. His parents were Plonka Joseph and Matecki Marianna.
The town of Grodzisko-Pleszew is nearby, but there are many such names in Poland.
Would appreciate your reply if you see any connection.
Thanks, Bernd Plonka in Germany.