Cylinder bores on mass produced engines don't all come out the same. Factories usually have the bores checked and depending on the amount off of tolerance, different pistons may be used. This, more than likely is the amount oversized the bore is. Another possibility could be a number used for balancing.
There are sometines different bearing sizes used on mass produced engines as well, again, depending on the tolerances the engineers give to the workers, here too, an assemblyline protocol is followed as well.
I am not saying this is true on the FE block, and these numbers ARE for any of those purposes, but it fits. Sometimes stampings were also used for line workers to identify over/undersized items needed for final assembly (I know GM used stamps for example, at least in the 80's)
If the bore is original and not worn down, see if this matches. It would be good to know.
Richard
