I don't normally use the start retard. I just decided to try it.
I do have the separate starter and ignition switches, which is how I normally start the car.
I have never broke one of these oil pump drives before. But I only ran a roller cam 1 season. That was my 540 KB, 440-1 head motor; which sold that fall.

I am using 10W-30 oil, and it was just after lunch, so the ambient was about 70 degrees.
The previous day I set the ignition timing (32 deg) and valve lash HOT. Just before lunch I verified the COLD 0.006" lash.
I will try to get a better picture of the break with my Olympus camera instead of my phone.
But it is, what it is. I just need to check around for any other signs of a problem.

During an early mock up of the block, I did insert this bronze gear drive in the block to check it turned smoothly in the block bushing.