The MSHD rerouted M-66 between Maple Grove and Nashville in mid-1953. In the changes, M-79 was extended along the new route of M-66 and then over M-214 to Hastings. M-66 was shifted off Assyria Road which was turned back to local control. Another realignment in 1954 shifted M-66 to the modern routing between the M-43 concurrency termini, removing M-43/M-66 from a section of M-50 in the process. The final section gravel section of M-66, approximately in length, was paved near Nashville in 1957. M-32 was extended along the northernmost section of M-66 in 1963.