You could use the cooler from the ST170 engine, I was gonna use it on mine but space did seem a bit tight and getting a nice run for the hoses looked like it was gonna be a little tricky, so I never bothered, could add it at a later date.

For the plumbing I used the cvh thermostat housing and connected it to heater matrix.
The pipe that comes off the bottom hose and runs around the back of the engine, do away with the Y piece and use a joiner to connect to heater matrix. If I was gonna run the cooler I would expect this would be the hose I would tap into/divert.