did cranks come under sized from the factory

yes

_________________
My truck is a Frankenstein creation
Built from the dead carcasses of others
And brought BACK TO LIFE!

When the factory uses undersize / oversize parts in an engine they stamp a code into the block, up by the ID number.
DD

is there any way of decodeing the numbers.

thanks

The codes are in the form of shapes, numbers and letters stamped into the ID Pad.
It is important to know the year of the engine because the symbols changed over the years.

Example: A 1966 SL6 with undersize crank journal(s) (from the factory) will have a Maltese Cross stamped into the ID pad followed by M-1-2-3 etc. indicating main journals #1,2,3 are undersize by .001. R-1-2-3 etc. indicate which rod journals are undersize.
A Maltese Cross followed by an "x" indicates that the journals are .010 undersize, M-10 means all mains are .010 u/s and R-10 would mean all rod journals are .010 u/s

There are other letters and shapes to indicate over / undersize cylinder bores, tappet bores etc. All this is spelled-out in the service manual for that year of engine.

One thing I have learned over the years is that this is just reference info., you need to check / measure the actual parts for their size before buying replacement bearings, rings, lifters etc.
DD