Calculate Incremental ID Based on Location in Grid

[EricErtl]

I have a feature class with 40 acre plots and want to create an incremental id for each 40 acre area based on its location.  I tried using the sort and calculate unique value geoprocessing script but the 40s are not in a perfect grid (forth row down on the eastern portion) so they don't increment correctly.  Does anyone have any experience with this type of dilemma?  I attached a screenshot of what I am trying to accomplish (I entered the IDs in manually).  I appreciate any help.  Thanks!