Pilot bushing direction

You may have 2 problems. Not sure if 273's did but 318's/ newer engines do which is:
1: As mentioned, hole from auto car may not be deep enough. Jig up bell on engine, measure carefully from face of bell to bottom of hole, then measure length of gearbox shaft to bell face and make sure it will clear

2: Some auto cranks are not fully finished bored for diameter. You used to get an undersized bushing to fit an "auto" crankshaft
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?