Broken 440 rocker shaft, anyone else?

If you had to use a lash cap something else is wrong. I'm going to repeat myself but your geometry is probably wrong and needs to be corrected.

If you are breaking retainers and such its from some harmonic in the valve train usually caused by a geometry problem. You can't buy parts good enough to live through stuff like that.
So true. Broken retainers and now a broken rocker shaft. I was standing next to Comp Cams Billy Godbold at a dyno contest. There was an engine running on the dyno and when it shut off he said, "Did you hear the valve train harmonics? It is going to die soon." Two runs later a rocker shaft broke.