My 273 had those little plugs in, and I know the motor had never been apart previously. Also, this engine does not have a "holey" bolt, but it does have the oil slinger on the crank snout for chain oiling.
I've never seen plugs in any unmolested early, 64-73, small block, and I've done too many to count... Someone may have added them during a timing chain swap? But as we all know, anything is possible...
