Can I just go to Autozone and get an ignition coil for my 96 mercuriser 5.7L?

You must use a high vibration coil in a marine application. A car has rubber mounts for the engine which reduce vibration stress on coil. A boat dosen't.

The T bolt ignition is supposed to use a "special" $40 coil.
I bought a $10 GM, external resistor coil at a car patrts store and it's worked fine for years.

I got a pair of the high output high zoot chrome coils from Parts Source (Canadian version of Auto Zone)a few yrs back for my carb 350s with T Bolt ignition......no probs

wondered the same thing as you at the time but the ones I took out sure looked like standard automotive stuff to me.

The coil is hard mounted to the engine, no rubber mount. A coil is a coil, is a coil. Although I prefer Accel stuff due to good insulator plastic.