I ground out what I think are the same plates early this year (if you can post a picture I will be able to confirm that).
If it is the same part, the two plates are connected at the bottom with steel strips that are glassed in with several layers of thick matt, and connected at the top by a steel bar. An absolute @#$% to remove completely, a better bet is to remove all the steel above the glass, and rebuild on top. I got through the main steel plates with a thick 4" metal grinder, and then pressed down as close to the hull as I could get, which left the area clear enough to work over. Rebuilding with enough strength is the kind of thing I leave to a professional as my glass skills are not good enough.
I did all this with the fuel tank and deck over it removed, going through that access hatch would be extremely painful, if possible. Grinding that close to a tank filled with fumes with your body stretching uncomfortably would have risks. Moving the fuel tank forward a few inches was fairly easy, I just removed one small piece of plywood bracing it (two screws); removing the fuel tank completely involves removing either the deck above it, or cutting access through one of the panels around it - although if it is original it may be close to the end of its life and need replacing soon (mine had pretty bad corrosion on the aft panel which I had not seen until it was out).
Good luck, not an easy task.
Gareth
Freyja E35 #241 1972