I bought a project car in pieces, one of which is a 454 long block. This motor is a Gen VI (cast into rear of block) and was originally a marine engine. (blue paint still visible on rear of block). There was no flex plate, so I ordered one from Summit, asking for a plate to fit a Gen VI with a T400 trans. Now that the motor is together and running, it feels out of balance. Does the fact that this was a marine application engine figure into this?? Could they have just sent me the wrong part?? Any theories would be appreciated!