eric
i had a similar problem on my w28 "narwhal", but mine wasnt nearly as bad as yours appears to be. my distortion was more or less in a fore and aft direction. yours appears to be all around. take your straightedge out on deck and it will probably show distortion there as well. also check to see if the aluminum mast step is rotated from vertical, mine was.
the mast is supported on a boss about 2" thick on top of the deck. the inside of the boss is formed with laminated plywood. on my boat a leak at the hole for the mast wiring, caused this plywood to turn to wet mush. the wide mast step pushed the rest of the deck down around the top of the compression post causing the deck to deflect up into the mush space. i sugget that you check your deck core material to see if it has turned to mush as well.
i removed my mast, dug the mush out of the boss and replaced it with solid epoxy and fiberglass scraps. (i have a picture of this somewhere) i then jacked up the deck using a 4x4 post and wedges from a platform that bridged the bilge. (dont jack off the bottom of the bilge! see below.) i also wedged the deck up off the bulkhead. i then cut about 1/4" off the top of the compression post and fabricated a stainless steel 't" beam to span across the top of the post onto the door jamb foreward of the head door. i then supported this jamb at bilge level with a smallish sort of stump under the liner onto the flat of the bilge. (this was probably not a good idea because the bilge at this lication is just a bit of plywood glassed over some foam).
i think the top flange on my ":t" beam was 1/4" x 4" about 2' long and the stem of the "t" was about 1/2" x 2". the mast end projected aft over the post to spread the deck load. the "t" part was fitted with a couple of brackets that i housed into the compression post and jamb and fastened with 14 ga screws. i may be able to provide some detail of this beam if you want and i can find them. depending on the state of your deck, you may need something wider that 4" across the top of the post.
i subsequently found that the short stump under the compression post below the liner was bearing on the thin glassed plywood that spans the bilge. the plywood ended at the edge of the lead ballast and caused a sheer tear in the flat of the bilge that allowed the keel space around the ballast to fill with water, but that's another story that i am still working on.
