Is it too late to fix these floor boards

Yes, what he said ^^^^^. Those floors are done as far as strength and integrity are concerned. Can you grind them and fiberglass them? Yes, but that's a hackers method and not the right way to fix them.
I done fiber glassed and POR15 mine back around 1985. Way back then I fixed the windshield leaks and installed brand new wiper pivots to stop the leaks prevent further damage. Yes brand new wiper pivots ordered from parts department at local Dodge dealer. Anyway going with full floor to repair mine now.

Make sure you run a hose over car and in wheel wells while interior is out to make sure water not leaking into car. Mine had a bad spot weld in rear wheel well water came in driving on wet roads caused rear floor board to rust out. Water leaks wet carpet = rotted out floor.

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