Just picture the scenario that would have to happen to break the Slant six rocker arm. Coil bind that would flatten the cam first after bending the push rod unless it's a hell of a push rod so then the next weakest thing would be the rocker or stock adjuster. Now it's a question of what kind of breakage though did it split at the tip is there an alignment issue and or is the adjuster side bending sideways. Etc is this one of these milled .100 heads with stock push rods and the adjusters backed off until they're barely threaded in the rocker arm?
