marinizing a snowmobile engine and drive setup?

Hello, I am building a 11 foot speed runabout for insane purposes and don`t know anything about marinizing a engine, I want to put a 500cc snowmobile engine in it and run this to a lower end of a outboard leg made up with homemade brackets, I am on a really tight budjet so this setup could be made to work, the boat will only weigh about 120 pounds empty, carry 2 people and be just a toy, I figure with the right prop I should be able to hit 40 mph easy,( thats my goal) I haven`t been able to find many web sites with imformation on this type of a project, What would I have to do to make the engine marinized? if it was not marinized what safety problems are involved, can I run a stainless steel exhaust into the water without damage to the engine and should I look for a lower end outboard of say around 40 Hp.Any help I may recieve will be greatly appreciated,
Thankyou Bill Pickering BC Canada.

 

this seems the easyest way to me

 

your asking for trouble. a snowmobile engine was designed to run at below frezzing temps. you will have to redesign the carb setup and exhaust. in my opinion it would never be reliable.