I had to buy a cooler from an auto parts supplier. The kit provided the Oil Cooler Mounting Plate and gaskets and hardware. I installed as insrtucted.This inclued removing some of the bottom flange on the cooler.
After the fact Note from experience: 1. I had issues with fitting cowling over the top mounted oil cooler. I cut off the top flange of the cooler like I saw that most builders reported in their builders logs. However my top cooler contacted (hindered) my horizontally cut Cowl. I tried may things and research many potential solutions but nothing worked. Later in talking to Sonex Tech Support I was told they had an different top mount oil cooler plate which was oart of the Onex kit that placed the oil cooler about a half inch further back on the engine. I had to buy it from Sonex (about $60) who would take my original mounting plate back in trade. The bottom line is it worked for me. 2. I chased an oil leak for several days, thinking it had to do with the gaskets not seating correctly. I probably took it of and reinstalled 10 times befor discovering the leak was a loose port allen screw on the mounting plate.
