[IIonPilgrimg]

Whittle it out with Sawzall and/or putty knife, chisel and hammer. Remove One Whole piece without damaging (much) the walls or outer hull.

 

[Griffin]

Has anyone tried installing thin fiberglass stringers embedded in the balsa floor? Even after repairing my Harvey’s floor, it still flexes more than I would like. I feel like it’s only a matter of time before it cracks again.

 

[IIonPilgrimg]

Recalling your posts of a year back, you've gone with a balsa/epoxy floor. A Harvey floor should flex and you can feel it under your feet (at speed).
If all is bonded into one coherent slab, I suspect you're over-thinking it. Flex cycles will have an effect over time... lots of it. But if the core is not compromised, all will be well for decades and epoxy was surely the better choice. Breakers have a channeled construction which stiffens the floor. It's also convex against the bottom. Tony has construction samples / photos and I'm sure he'd be happy to share thoughts.