the thickness of the material looks suspect surely? if you think about how the initial force of the push-rod is acting on that rocker, the place where it has failed is under a tremendous tensile load, just as the top piece, which is substatially thicker, is under a compressive force. to be so thin, and subject to such tensile forces, it doesn't surprise me to see a failure like that. compared a stock iron rocker, that design looks weak to me. they should warranty a failure like that. unless you have mega strong springs and a radical cam, that should not have happened IMO.
'68 GT390 fastback. 445 stroker. all roller. 478/505. C6. 3.25 trac-loc.