I gathered info regarding oilcooler set up for the C-90 engine. I still struggle to find a proven oilcooler adapter for the left side of the crankcase where the flange is located at. I might have found an adapter now that comes from the O-200D. Checking with some experienced engine builders wether it would fit. I really consider putting in an oilcooler.
The adpater I'm considering is coming from Teledyne Continental Aero with the part number: 657686. I enables to install the cooler on the firewall. The adapter includes already a pressure regulator. We don't want the cooler to be working while the oil is still cold. Due to the higher oilpressure, the ball moves against a spring and blocks the way to the cooler. Keep it simple!!