I did that with my 1990 176. Used Marine plywood and contacted Champion for the matching carpet.... In your case, the matching carpet might be difficult to acquire, but probably possible to get close to the color from marine supply companies. I measured width all along the area I wanted to fill with deck, and then built legs to support at the exact height of the rest of the deck...worked great!

Sorry, no pictures, but it was not difficult... Tracy's plan sounds even better!!!