Where do you get "an undersized bushing"?
I just measured my 92 LA roller motor crankshaft depth. 2 3/4 inches deep.
I don't really think if you drill the back of the crank you're going to hit an oil passage. There is no oil passage that goes thru the center of the crank main journal. The number 8 rod journal is fed at an angle from the main. Chrysler drilled cranks for years for the pilot bushings.
Isn't there a roller bearing that takes the place of the bronze bushing and makes shifting easier?