Here's the factory brochure on your boat:
http://www.fourwinns.com/uploads/2017/2/1985catalog.pdf
Scroll down to the last page as it lays out what you're about to find under the floor - wood stringers, wood floor with foam. Unless this boat is a time capsule that spent it's entire life in an indoor showroom, I'd be willing to wager you have a much larger project on your hands than just the interior.
So....I'd start by reviewing the structure of the boat before diving in on trim work as boats rot from the bottom up, not the top down. Make sure you have a sound base to install all the trim. Knocking with a hammer won't cut it here. Drill samples in the stringers as low as you can go. Same goes for the transom but don't go through the outer hull! Hopefully you get clean shavings which you can then fill back up with 4200/5200. Anything else, and its going to be a stopping point where you will want to consider if you want to restore the boat or not.
As for finding original interior...you're probably better off going with all new unless you find someone with a mint boat who's about to haul it away to the nearest dump.
Post some pictures up after your 3rd post, you're at 2 now so try after your next one, so we can all see what you are working with.