No spark/replaced coil. Are you running conventional points and condenser or Electronic Pertronix Ignition? Pertronix have been know to fail under heat condition.
https://itstillruns.com/do-tes...gnition-7993715.html
It's got to be as hot in TX as NW FL last couple weeks! There was a thread here to build "a prop" that keeps rear lid open a few inches for extra air.