New and improved with pictures...
I struggled with my plan for how to stretch the hull by 12.5 scale feet...luckily, the Trumpeter kit has a long cylinder that runs down the middle. It is long enough that if I slide it forward some, it will stretch all the way across the extension with space t add multiple attachment points for the bow section that is moving forward. First I broke out the old contour gauge and started making some "ribs" for the inside of the hull with appropriate cutouts for the "pressure hull" cylinder to use it for alignment.
I ended up making six copies of the largest one to allow two on each side to provide internal structure to the extension and then one on each side at the after end of the bow section. These three stations are the same because the extension that was inserted was a continuous section piece that didn't blend into the form of the hull at all. The next station forward also has the cutout for the cylinder to control alignment. The two forward most stations are just to provide structure for the rest of the work that needs to be done on the bow.
So, there you have it for now. That is what you can get done in a BOQ room on TAD with no power tools or major equipment.
I also have to fill the limber holes and redo ones appropriate to TIRU as a Guppy III. So, some plastic card was put in place (for backing of the eventual fill) as well as some internal stiffeners (spare sprue). The "stiffeners" are to maintain the shape when I cut out most of the deck and replace it with plastic card. Only about 30% of the kit deck will remain (maybe even less).
Here's a look at some of the work on the forward decking. I am trimming wider of the plans to leave space and material for eventual sanding of the curvature of the deck edge. I will also have to transplant a piece of the kit deck from the after section up to the rear ed of the forward section to get rid of some detail lost to an alignment part.