Here's what I'm thinking

[garagenc]

Kam

How is it up there at nswc?

I believe you should be able to tie the new stringer/frames into the existing floor stringers.

When you move the temp weight to find out the balance point see if you can leave the CC in it's original place; normally they are installed just fwd/aft of the fulcrum point (center of gravity) to keep the nose of the boat from staying up or down.