I have a 360 LA from the 70s. It has been rebuilt with a Comp Xtreme energy (206/212 @ .050 .432/.444) cam and almost too high compression. It has about 170 to 180 psi cranking pressure. I have had this combo for about 13 years now and has ran fine with 12° initial and around 30 degrees total. Lately, like the last fill up it has been pinging something terrible. I thought, at first, that it was the MSD 6AL box as I have had one fail in the past. The MSD that failed was causing the timing to jump to an extreme advance and run and ping terrible. At that time I switched back to the factory module and it would run fine. I replaced the MSD box and it was back to normal. This time I switched back to the factory setup and still the same issue. I always have to run supreme fuel so I thought I had put regular in by mistake. I have done this in the past too, but I am able to put a couple of bottles of octane boost and remedy the problem. This time however it didn't help. I also thought maybe I just got some really crappy fuel and I needed to completely start over. So I ran it near empty and replaced it with supreme (I paid careful attention this time) and still the same result.

What am I missing, what could cause this terrible ping in just the span of a tank of fuel. Its bad enough you can barely drive 55 and even then if you hit a small hill it will start pinging and you will have to slow down to 45 or maybe less sometimes. Any help would be appreciated.