Re: How much deck over the cabin do I remove?
Pictures will help a lot.. you're there now (post count) .. probably best to use a site like Photobucket.com rather than attach pics via the SN option. Pictures will be bigger, clearer and show up full size in your post. Be sure to use the IMG CODE linking option.
Though much harder to work at, leaving the outer skin intact and trying to do the job from inside will leave a much better looking result... btw plywood is not the best option here, water easily migrates horizontally in plywood, properly installed balsa core would be better, along with some foam coring materials.
1984 Fast/Nicholson 345 "FastForward"
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)