Think they say 500hp/6000rpm limit. You definitely were over their limit in both areas. haaaa prob piston speed and piston weight has something to do with the abuse the will live under.
On the boosted set up, did it go lean before the bomb went off, or did you squeeze it a Lil harder than you normally did in the RPM department? We're all the valves still in the head after the autopsy? Reason I ask is I over revved a 340 once and did the same thing with stock rods. After the autopsy I found out it actually dropped a valve which took out the piston, cyl wall cam and everything else in between. Sounded like a Glass jar of marbles when it happened.... So much crap went everywhere. When I put the new stroker in there were chunks of the old engine flying out the exhaust. Big pieces too!