These are a little tough to repair, but not impossible. Part of the problem is that it took years for it to do that.
What we have done in the past is to use about a dozen bottle Jacks (you could use virtually any jack capable of lifting about 1,000 pounds, but I had the Jacks on hand and they're dirt cheap) and block to the floor or over the stringers every few feet down the sides and on a warm day (or use heaters) slowly (like over a few days) start to lift the deck. Too fast and you will fracture the glass and gel coat, which may occur anyway, but the slower the better.
Once you get it where you want it, go a little bit more (like a quarter inch l and let it sit in the sun for about a month. Meanwhile, make templates of some bulkheads. One forward of the dash, one about midway and one about at the front of the engine. These have to be made so the wood has about an 1/8" air gap all the way around.
After the settling time has lapsed, drop the Jacks so things are uniform and yo your liking and tab in the new parts, sanding/trimming as necessary.
Once those are in place, glass the heck out of them. Let it cure for a few days and you should be good.
Big projects don't always have the greatest reward, but it will be good for the rest of its time on this planet.
Good luck.
GT
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