I'm thinking about replacing my blown up 580 with a cheap 657 I found. I just have some questions that I am unable to find the answers online. First off, what adjustments/modification do I need to make to the cooling system? I noticed on the 657 that there are 2 ports on the head and an additional port on the exhaust near the water box. Secondly, do I have to change the pitch of the impeller due to the larger engine? Can I just put the twin carbs with the manifold from the 580 and put them on 657, or will I have to change the jets on the carbs? Anyways, a rebuild of the 580 would cost me $350. The guy wants $250 for the 657. I also have another guy who is selling a good 580 for $300. Is the 657 worth it? I apologize for asking a boatload of questions in one thread haha. Other notes, the 580 is white and the 657 is a 657, not a 657x, so I know the stator wires will match with the electronics.