Update: I would say my gut is at least half way complete. Overall the damage is not too bad. I have repeatedly confirmed the port main stringer and bulkhead are good. I have cut back the aft bulkhead to good wood on either side. Furthermore, I have cut out pretty much all the remaining fiberglass tabbing in this area. I also cut the engine stingers out in the rear portion to skin the transom, which I have also done. The center, lower portion was mush and wet, but there seems to be lots of good wood too. I am in favor of a partial replacement of course. Here are some pics:
Center transom:
Most of the rotted wood is dug out, I am still trying to figure out how to cut the rest out of the transom. I want to use the oscillating tool , but I don't want to cut through the hull. Would a grinder work better?
See this little block??? IT'S ALUMINUM. I do not know it's purpose, but it keeps the (dry) foam off the hull. I am also guessing the main stringer buts up against it. I drilled into it because it was a bit soft, I knew something was up, but being aluminum makes sense. I also can't get it to budge so I'm going to leave it and rebuild around it as the foam is fine.
Here is a larger view of the same main stringer. Note the spacing blocks:
Port side of aft bulkhead cut back to good wood:
Starboard side cut back to good wood:
Stringer skins practically gutted near bulkhead:
Drilled holes in engine hatch, all solid:
Not the design of the hatch, very weak in the center. I like the pvc pipe idea, but it may interfere with my risers:
