I had the same thing happen on my red 70' Sixpack Charger. It would just die whenever it wanted to. Most of the time when it was hot (at running temp). It turned out to be the parts store coil over heating. I bought a MSD blaster 2 coil & painted it black. That lasted several years but eventally started doing it again. I am back to another parts store coil & all has been fine for several more years.
I think it has something to do with the location of the coil in the factory bracket that causes it to over heat over time????? My 440 4 BBL cars never do this with the coil mounted further up front hanging off of the front of the intake manifold.