I goofed up and put the jumper cables on backwards

now my boat will not start. I had the engine checked out and was informed it was the ECM. I took it to have a new fuel pump installed because I thought that was the issue and ended up having a cracked block.. Unfortunately the engine was rebuilt and the fuel pump is brand new. Now it will still not run. I have had so much work done to the boat it is killing me. The last thing said was that I need a new ecm but the one in the boat does not match the serial number any more. I cannot buy new ecms until I find the right one that is the match. Any suggestions will help emensly? I am considering going carb but not sure exactly what the process will be. Please help in any way....Thanks in advacne
