Not sure who or if anyone made water cooled headers for the Picco Hydro 90's but I can tell you how I made them for my engines many years ago. Get some 5/32" ( O.D. ) copper tubing and anneal it with a propane torch ( heat it until it just turns red then let it cool ). Then you can make three wraps around the exhaust header, cutting it off so that you have an inlet and an outlet for water. Clean the header and tubing real good with alcohol or some thinner and glue the tubing to the header with some high temperature red silicone. This will give your exhaust couplers a lot more life. Hope this helps.
Dick Tyndall