Are you saying you took it to 8500 on initial startup? Yes, 8500 is a lot of rpm for a big block, or anything else,actually. For that kind of revs, you want to break it in good, and have top drawer components (which you seem to have). The crossdrilling idea would help, but in your case, failure seems to have come too soon for that to help. Are the rods distorting? Like, the ones that don't spin the shells, do they need resizing again?