Mystery solved. It is the way the inside of the crank end was milled. They left a raised lip at the bottom of the hole. No plug, just steel. I guess the drill bit I used to drill out the pilot bushing was sharper then I thought to leave a scuff mark.

1954 Chevy 3104 3 Window Hydra-Matic in my family for over 60 Years

Once in a while you get shown the light in the strangest of places if you look at it right... "Scarlet Begonias" Grateful Dead 1974