Well today I think I should rename Lincoln Shipyard to something like "The Butchery".
This morning I started by soaking the part on which the operation was to be performed in hot water - directly against my own advice to
@Nomad Mark. The reason I did this was only because this is a
@Kolderstok kit and because I have implicit faith in the quality of the materials. Thereafter it was a case of painstakingly wedging the Xacto blade between the transom and the planking and leveraging it in further and further, until it wouldn't go any further. More soaking in hot water and onwards. Eventually ...

Now I could clearly see just what a mess I have made of this part.

Scrap wood was then sawed to fit into the openings and glued in place.
And then I changed tack. Instead of immediately planking the transom, which would then mean an exact repeat of my initial attempt, I decided to first cut out the ports in the transom. Some wise man once said that the definition of insanity is to repeat the same thing twice and then to expect a different outcome.

Here is my transom doing its best impersonation of the evil "Falconetti" from Rich Man, Poor Man. Oh and by the way, if you think you are seeing a different wooden plug on the right to the one, I have shown you before, you are right. I messed that up too and had to replug it.
@rtibbs Ron, have you got special coins for Do-Overs while you are doing a Do-Over?

Both ports cut-out. You need to squint your eyes and focus only on the light shining through, otherwise it will still look like the dog's breakfast. I have cut them out inside the lines to allow for some fine-tuning once the cut-outs are finished. The idea is obviously that I will now drill my pilot holes from the back of the transom and score the wood as far as I can before flipping it over to do the final cutting.

And planked. As you can see, I haven't done any sanding or finishing to the planking. I didn't use any clamps this time so now the glue just has to dry properly until tomorrow morning before I will make attempt #2.