Seaplane down off Miami Beach....

I'm wondering if fitting turbine engines on the old airframes
didn't pull something loose in the wing/mount.

Turbines run a whole lot smoother than the round Pratts that were on
originally. They don't have the power pulses that radial engines have.
I'd agree with the other posters that it sounds more like a
leaking/broken fuel fitting that went bad, ignited and led to
structural failure.