I've noticed that this dimension (as index of crank stiffness or resistance to bending) is frequently quoted as:
Journal Overlap = ½ (Main journal OD + Rod journal OD - Stroke length)
This is not only an approximate, but has a built-in error favoring one end of the scale WRT journal sizes.
I furnish the somewhat complex math (plane geometry) for a better method (used by GM for many years AFAIK) on my site here:
http://victorylibrary.com/mopar/journal.htm