The sternpost was left long intentionally because it is always easier to shorten a timber than it is to extend one. As you can see, I there is plenty of excess on the sternpost to be cut off.
The transom and sternpost are supposed to end at the level of the sheer, and these timbers need to be cut down.
To mark the cut line for the sternpost, I strung a tape measure across from sheer to sheer and marked the line where the tape measure crossed the sternpost.
Using a hand saw, I carefully cut along this line. I tried my very best to ensure that the saw cut parallel to the sheer and the sternpost was kept in line with the other lines of the dinghy.
With the sterpost cut, the next step will be to cut the transom down to size. You can see the hashed line running across the inside of the transom, this is where I anticipate that the top of the transom will end. The sternpost was cut higher than this point because it is always easier to cut it lower rather than to make it longer.