I would think that tieing in the center stringer to the transom would be important. I'm not sure what power plant you are planning on going with but if it is outboard then I would add a knee to the center stringer. If you go back with inboard/outboard then you may not have the room. Here's a couple of pictures of what I did. I have a 20' sf and will be hanging an outboard on the transom notch. I used coosa for the transom and the knee. I put a small limber hole in the base of the knee. If you went this route you could easily make the hole larger to accomodate the transom drain. Hope this helps.
[image]
[/image]
[image]
[/image]