I have the chance to get a motor from a guy at a very good price. The informatiom supplied by the seller is that it is a early 1980's motor.The problem I'm having is the guy claims it is a 400 cid but the casting number on the block is 3970010 (80-82) and after researching casting number it is shown as a 350 cid block. Can a 400 cid be built from a 350 cid block? is there any way to tell what motor it is without tearing it down.