The block has 3 holes that intersect on the mains. Of those 3 holes the one that gets the :shot" of oil is the hole on the "tab" side.
All my engines I drill a hole right through the main bearing in those locations . Then take a jewlers file and de bur.
Its a old Dan Whitmore trick. He said if its not done your rods (6 and 4, maybe 2 ?) get starved of oil at high RPM.
The Clevite style bearings are the worst with their round oil hole. Oil hits the back of the bearing, moves over and goes on through. Make it a straight shot.
FM Race bearings with their slot are a little better but I drill them too.
I have never hurt a main or rod bearing doing this.
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