The first thing I want you to do is take that crappy looking ground wire off from the battery and throw it away.
I've seen this happen with a negative ground cable which had broken down in the center. (Looking at the black tape on the red ground, looks like vomit to me.) High resistance in the ground circuit caused anything that could provide ground to provide ground...like points, to provide a ground and of course the points can't handle a ground path for the entire vehicle.
Ground goes for the least resistance and if there's high resistance in the cable..only seen under load, then the points are a lot easier to hammer high amps through.
I bought a new ground cable with a pigtail (NAPA), added a 10G wire right to the volt regulator (-) and a 10G wire (-) from the intake manifold to the firewall.
Also, my battery is turned around compared to yours.
That would run you about 20 bucks total to give it a shot.
Also, rotate your positive cables up a bit on the starter solenoid. I can't tell how close they are to arcing out fender.