Way to much timing and with Vortec heads we only need around 30 to 32 degrees of total timing.
Your balancer should be degreed with a 32 degree make and check it at the RPM where you have the most timing. And go from there. I don't use vac. advance on a performance engine. But do change the curve with springs.
Your tune up killed those pistons and your lucky the guy is standing behind this as its not his fault at all!!!!!