One of the "defects" I have considered in modern rebuilding is that a "ground crank" may be fine for use with pressurized lubrication (i.e. the crank journals are literally "buoyed" upon a pressure film of oil) and surface roughness becomes inconsequential to the life of the assembly. But modern ground cranks don't work nearly so well on a boundary lubrication situation like Ford's steel on babbitt.
Ford "superfinished" the crankshafts to achieve an original surface roughness almost unachievable at commercial crank grinders today. The "break in" of engines on the test stand (extant picture) was almost more for the "rest" of the motor. Things which Ford couldn't control in manufacturing, things like cylinder walls/ring match.
The 26K original mile AA truck chassis comes to mind. Engine was "loose" but very drive-able - not quite into the "whuppa-whuppa" stage. I drove it before the body was removed and I took the rolling powered chassis home. But that engine had probably NEVER been opened for a shim adjustment.
One person whose knowledge of these things I respect considered that the 75K was about the life of ANY motor without a filter/air cleaner - so Ford MAY have had that in mind. But the question may be was the crankshaft/lower end sized to the life of the unfiltered cylinders above it, or the other way around?
As to life - expect to change out shims perhaps three times in a 75K life of the motor. My truck (avatar) was on its 2nd motor (painted red) and that thoroughly worn out. (probably an Allstate Motor Replacement) The odometer read 43K miles (i.e. 143K miles)
I hope my rebuilder Knight Automotive can enter in and comment here. He's retired now but stops in occasionally for exactly that.
Six Million Dollar Man comes to mind:
We can rebuild him. We have the technology. We can make him better, than he was. Better, stronger, faster.
The red paint will help...
Joe K