That last photo is significant. The factory dual four Carter intake was worthless to Nascar, and really most racers. I am aware that the single Holley solid tappet engines were widely available not only via parts, but also directly from Chrysler in you were in their network. As stated, these engines were blown up and replaced very often. The numbers must have been pretty high.
I know there is so much mistique, legend, controversy and all that but this was just an industry. These were machines in a large system and when you wear out or break it, there is a system to replace it. When one of my paint guns no longer sprays well, get a new one. This is history, I suppose. It can be kind of interesting.