What I did, faced with that issue, is measure each and every hose. Each boat is different, so there's really now way that you can buy a "kit", so make the effort to find both the size and length of the hoses. Some are 5/8", some are 7/8", like from the freshwater coolant pump to the HX.
You'll have to find a local source for quality hoses.
You'll need new coolant, too. Use distilled water - get it at Safeway when you go to buy your beer!
Once you make the changes, you'll have to BURP the engine. Like this:
Engine Overheating 101 - How to Burp Your Engine (Reply #6)
http://c34.org/bbs/index.php/topic,4518.msg26462.html#msg26462