An old post, but search for HD part # 62868-99a, the instructions are on the web and you can read how they were installed. This particular kit was for years 97-2002, both late model evo's and twin cams. What made this one year specific was because of the way the voltage regulator was mounted as the cooler's mounting bolts shared the regulator mounting bolts. This kit's cooler hoses & thermostat where installed on the return line between the oil pump and the oil pan.

Anything on the return line is not going to have any affect on oil pressure and because of the thermostat, on a cold engine the oil bypasses the cooler until the oil gets up to operating temp.