I would get a copy of a grant deed for the property. Often times, at least out here in the West, the deeds would be more descriptive than the plat. Now, if the deed's description is just "Lot 80 of Grover Estates No. 1", then Michael's method would be used.
While the boundary is described with N, S, E, W directions, the internal lots have varying lengths for the side lot lines. This indicates that the roads are not running true N/S.