I currently have a 454 Mag that has the exhaust exiting through the outdrive that I was thinking about converting to through transom exhaust. Is this a complicated process? What kind of headers would have I have to buy for an I/O to go to through transom exhaust? What would happen to the exhaust port coming through the out drive? Is there a plug of some sort that is sold that is used to block water from coming in? What kind of HP gains would be achieved or lost? Any help is greatly appreciated.