I did the same thing with the back seat when my '96 190 seat caved. The wood lasted in the boat exactly 1 month before I ordered a sheet of that honeycomb aluminum and made the seat out of that. I laminated 2- 3/4" sheets pf plywood together to get it strong enough to support the weight, but it was just too stinkin' heavy. It looks like you added a center block to support the seat in the middle and allowed yourself to make the seat bottom out of a single sheet of 3/4". A much better idea than mine!
Also, I had a few of those threaded inserts pull out of the dash. I ended up drilling them out and putting in well nuts I got from McMaster Carr. It looks like your dash is torn around the inserts, so it might just be easier to pull the WHOLE dash out of the boat and install fender washers and nuts on the back side of the dash. This is the way the newer dash panels are installed.