Thanks for all the advice so far.

I'm leaning towards the Mancini--badged Harlan Sharp set at this point. Still pondering a switch to 1.6 ratio.

I found this in a previous thread about the 440 Source Rockers (sounds exactly like what happened with me):

"The issue with the alum. body offshore rockers was the spindle the roller tips turns on is brittle and is breaking. Once broken the rocker body design can/will push on the retainer and pop the valve locks off the valve, the valve drops into the cylinder and one can guess the rest."

At least I didn't drop a valve.