Do you know what head gaskets were used and if the pistons ended up below deck at all? Reason I asked is I had a 360 with similar combo as yours; small Lunati Voodoo cam (213/220 @ .050") and a measured 10.4:1 compression with iron Magnum heads. It lasted about 30k miles but I always had issues with pinging; finally one day it busted a ring land and cracked the cylinder wall when I floored it to pass someone on the freeway. In hindsight I should have been more on-the-ball with ignition timing, should've modified the advance curve for less total and more initial and eased up on the vacuum advance. I'd just hate for someone else to go through the same scenario.