One of the things I know causes some MSD failures, is starting them on a dead or near dead battery. The current spike must fry somthing in there. Although I have had my one 7AL2 for 25 years now in my street car, I have killed many 6AL's with exactly this issue...
I've hurt at least 2 of my old 6AL boxes from low battery trying to start. That may be what happened to this 6530 box, not sure. It's odd what it did though...ran fine until the box got warm, then it hit a limiter at 4500 rpm. The 6AL boxes when hurt will just die...no spark at all.
