I think you need to try and get ahold of Bill Scott of Precision Engine. He holds STC SA00985CH which covers the following –
“Replace Lycoming O-235-C2C with O-235-K2C engine or Lycoming O-235-C2C engine modified by Precision Engine STC SE00988CH.”
He has been a bit hard to get ahold of the last few years, Roscoe helped me last year when I was trying to get another STC from him.