Steve,
The floor boards and stringers in your boat are not stock/standard GBI  
construction. Somewhere along the line someone has done a very poor job of  
rebuilding that part of your boat. Particle board is way to flimsy to use as a  
stringer, even when it is glued together to the correct thickness. My floor  boards 
are marine grade plywood and have withstood some real abuse over the  years.
There are others on the list that have replaced the same parts and are more  
knowledgeable than I am. Hopefully they will see you post and tell you what 
you  need to know.
 
Rummy